changeset 50848:bd6b78feb6a3

8195097: Make it possible to process StringTable outside safepoint Reviewed-by: coleenp, gziemski, iklam, jiangli
author rehn
date Thu, 07 Jun 2018 14:11:56 +0200
parents db65921e9a9b
children 39ca7558bc43
files src/hotspot/share/classfile/stringTable.cpp src/hotspot/share/classfile/stringTable.hpp src/hotspot/share/gc/cms/cmsHeap.cpp src/hotspot/share/gc/cms/cmsHeap.hpp src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp src/hotspot/share/gc/cms/parNewGeneration.cpp src/hotspot/share/gc/cms/parNewGeneration.hpp src/hotspot/share/gc/g1/g1CollectedHeap.cpp src/hotspot/share/gc/g1/g1RootProcessor.cpp src/hotspot/share/gc/g1/g1RootProcessor.hpp src/hotspot/share/gc/shared/genCollectedHeap.cpp src/hotspot/share/gc/shared/genCollectedHeap.hpp src/hotspot/share/gc/shared/strongRootsScope.cpp src/hotspot/share/memory/metaspaceShared.cpp src/hotspot/share/oops/weakHandle.cpp src/hotspot/share/oops/weakHandle.hpp src/hotspot/share/oops/weakHandle.inline.hpp src/hotspot/share/runtime/globals.hpp src/hotspot/share/runtime/java.cpp src/hotspot/share/runtime/mutexLocker.cpp src/hotspot/share/runtime/mutexLocker.hpp src/hotspot/share/runtime/serviceThread.cpp src/hotspot/share/runtime/vmStructs.cpp src/hotspot/share/utilities/concurrentHashTable.hpp src/hotspot/share/utilities/concurrentHashTable.inline.hpp src/hotspot/share/utilities/concurrentHashTableTasks.inline.hpp src/hotspot/share/utilities/globalDefinitions.hpp src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/memory/StringTable.java src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/VM.java src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/tools/HeapSummary.java test/hotspot/gtest/utilities/test_concurrentHashtable.cpp
diffstat 31 files changed, 897 insertions(+), 828 deletions(-) [+]
line wrap: on
line diff
--- a/src/hotspot/share/classfile/stringTable.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/classfile/stringTable.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -29,7 +29,10 @@
 #include "classfile/stringTable.hpp"
 #include "classfile/systemDictionary.hpp"
 #include "gc/shared/collectedHeap.hpp"
+#include "gc/shared/oopStorage.inline.hpp"
+#include "gc/shared/oopStorageParState.inline.hpp"
 #include "logging/log.hpp"
+#include "logging/logStream.hpp"
 #include "memory/allocation.inline.hpp"
 #include "memory/filemap.hpp"
 #include "memory/metaspaceShared.hpp"
@@ -38,171 +41,196 @@
 #include "oops/access.inline.hpp"
 #include "oops/oop.inline.hpp"
 #include "oops/typeArrayOop.inline.hpp"
+#include "oops/weakHandle.inline.hpp"
 #include "runtime/atomic.hpp"
 #include "runtime/handles.inline.hpp"
 #include "runtime/mutexLocker.hpp"
 #include "runtime/safepointVerifiers.hpp"
+#include "runtime/timerTrace.hpp"
+#include "runtime/interfaceSupport.inline.hpp"
 #include "services/diagnosticCommand.hpp"
-#include "utilities/hashtable.inline.hpp"
+#include "utilities/concurrentHashTable.inline.hpp"
+#include "utilities/concurrentHashTableTasks.inline.hpp"
 #include "utilities/macros.hpp"
 
-// the number of buckets a thread claims
-const int ClaimChunkSize = 32;
-
-#ifdef ASSERT
-class StableMemoryChecker : public StackObj {
-  enum { _bufsize = wordSize*4 };
-
-  address _region;
-  jint    _size;
-  u1      _save_buf[_bufsize];
-
-  int sample(u1* save_buf) {
-    if (_size <= _bufsize) {
-      memcpy(save_buf, _region, _size);
-      return _size;
-    } else {
-      // copy head and tail
-      memcpy(&save_buf[0],          _region,                      _bufsize/2);
-      memcpy(&save_buf[_bufsize/2], _region + _size - _bufsize/2, _bufsize/2);
-      return (_bufsize/2)*2;
-    }
-  }
-
- public:
-  StableMemoryChecker(const void* region, jint size) {
-    _region = (address) region;
-    _size   = size;
-    sample(_save_buf);
-  }
-
-  bool verify() {
-    u1 check_buf[sizeof(_save_buf)];
-    int check_size = sample(check_buf);
-    return (0 == memcmp(_save_buf, check_buf, check_size));
-  }
-
-  void set_region(const void* region) { _region = (address) region; }
-};
-#endif
-
+// We prefer short chains of avg 2
+#define PREF_AVG_LIST_LEN   2
+// 2^24 is max size
+#define END_SIZE           24
+// If a chain gets to 32 something might be wrong
+#define REHASH_LEN         32
+// If we have as many dead items as 50% of the number of bucket
+#define CLEAN_DEAD_HIGH_WATER_MARK 0.5
 
 // --------------------------------------------------------------------------
 StringTable* StringTable::_the_table = NULL;
 bool StringTable::_shared_string_mapped = false;
-bool StringTable::_needs_rehashing = false;
+CompactHashtable<oop, char> StringTable::_shared_table;
+bool StringTable::_alt_hash = false;
 
-volatile int StringTable::_parallel_claimed_idx = 0;
+static juint murmur_seed = 0;
 
-CompactHashtable<oop, char> StringTable::_shared_table;
-
-// Pick hashing algorithm
-unsigned int StringTable::hash_string(const jchar* s, int len) {
-  return use_alternate_hashcode() ? alt_hash_string(s, len) :
-                                    java_lang_String::hash_code(s, len);
+uintx hash_string(const jchar* s, int len, bool useAlt) {
+  return  useAlt ?
+    AltHashing::murmur3_32(murmur_seed, s, len) :
+    java_lang_String::hash_code(s, len);
 }
 
-unsigned int StringTable::alt_hash_string(const jchar* s, int len) {
-  return AltHashing::murmur3_32(seed(), s, len);
+class StringTableConfig : public StringTableHash::BaseConfig {
+ private:
+ public:
+  static uintx get_hash(WeakHandle<vm_string_table_data> const& value,
+                        bool* is_dead) {
+    EXCEPTION_MARK;
+    oop val_oop = value.peek();
+    if (val_oop == NULL) {
+      *is_dead = true;
+      return 0;
+    }
+    *is_dead = false;
+    ResourceMark rm(THREAD);
+    // All String oops are hashed as unicode
+    int length;
+    jchar* chars = java_lang_String::as_unicode_string(val_oop, length, THREAD);
+    if (chars != NULL) {
+      return hash_string(chars, length, StringTable::_alt_hash);
+    }
+    vm_exit_out_of_memory(length, OOM_MALLOC_ERROR, "get hash from oop");
+    return 0;
+  }
+  // We use default allocation/deallocation but counted
+  static void* allocate_node(size_t size,
+                             WeakHandle<vm_string_table_data> const& value) {
+    StringTable::item_added();
+    return StringTableHash::BaseConfig::allocate_node(size, value);
+  }
+  static void free_node(void* memory,
+                        WeakHandle<vm_string_table_data> const& value) {
+    value.release();
+    StringTableHash::BaseConfig::free_node(memory, value);
+    StringTable::item_removed();
+  }
+};
+
+class StringTableLookupJchar : StackObj {
+ private:
+  Thread* _thread;
+  uintx _hash;
+  int _len;
+  const jchar* _str;
+  Handle _found;
+
+ public:
+  StringTableLookupJchar(Thread* thread, uintx hash, const jchar* key, int len)
+    : _thread(thread), _hash(hash), _str(key), _len(len) {
+  }
+  uintx get_hash() const {
+    return _hash;
+  }
+  bool equals(WeakHandle<vm_string_table_data>* value, bool* is_dead) {
+    oop val_oop = value->peek();
+    if (val_oop == NULL) {
+      // dead oop, mark this hash dead for cleaning
+      *is_dead = true;
+      return false;
+    }
+    bool equals = java_lang_String::equals(val_oop, (jchar*)_str, _len);
+    if (!equals) {
+      return false;
+    }
+    // Need to resolve weak handle and Handleize through possible safepoint.
+     _found = Handle(_thread, value->resolve());
+    return true;
+  }
+};
+
+class StringTableLookupOop : public StackObj {
+ private:
+  Thread* _thread;
+  uintx _hash;
+  Handle _find;
+  Handle _found;  // Might be a different oop with the same value that's already
+                  // in the table, which is the point.
+ public:
+  StringTableLookupOop(Thread* thread, uintx hash, Handle handle)
+    : _thread(thread), _hash(hash), _find(handle) { }
+
+  uintx get_hash() const {
+    return _hash;
+  }
+
+  bool equals(WeakHandle<vm_string_table_data>* value, bool* is_dead) {
+    oop val_oop = value->peek();
+    if (val_oop == NULL) {
+      // dead oop, mark this hash dead for cleaning
+      *is_dead = true;
+      return false;
+    }
+    bool equals = java_lang_String::equals(_find(), val_oop);
+    if (!equals) {
+      return false;
+    }
+    // Need to resolve weak handle and Handleize through possible safepoint.
+    _found = Handle(_thread, value->resolve());
+    return true;
+  }
+};
+
+static size_t ceil_pow_2(uintx val) {
+  size_t ret;
+  for (ret = 1; ((size_t)1 << ret) < val; ++ret);
+  return ret;
 }
 
-unsigned int StringTable::hash_string(oop string) {
-  EXCEPTION_MARK;
-  if (string == NULL) {
-    return hash_string((jchar*)NULL, 0);
-  }
-  ResourceMark rm(THREAD);
-  // All String oops are hashed as unicode
-  int length;
-  jchar* chars = java_lang_String::as_unicode_string(string, length, THREAD);
-  if (chars != NULL) {
-    return hash_string(chars, length);
-  } else {
-    vm_exit_out_of_memory(length, OOM_MALLOC_ERROR, "unable to create Unicode string for verification");
-    return 0;
-  }
+StringTable::StringTable() : _local_table(NULL), _current_size(0), _has_work(0),
+  _needs_rehashing(false), _weak_handles(NULL), _items(0), _uncleaned_items(0) {
+  _weak_handles = new OopStorage("StringTable weak",
+                                 StringTableWeakAlloc_lock,
+                                 StringTableWeakActive_lock);
+  size_t start_size_log_2 = ceil_pow_2(StringTableSize);
+  _current_size = ((size_t)1) << start_size_log_2;
+  log_trace(stringtable)("Start size: " SIZE_FORMAT " (" SIZE_FORMAT ")",
+                         _current_size, start_size_log_2);
+  _local_table = new StringTableHash(start_size_log_2, END_SIZE, REHASH_LEN);
 }
 
-oop StringTable::string_object(HashtableEntry<oop, mtSymbol>* entry) {
-  return RootAccess<ON_PHANTOM_OOP_REF>::oop_load(entry->literal_addr());
+size_t StringTable::item_added() {
+  return Atomic::add((size_t)1, &(the_table()->_items));
 }
 
-oop StringTable::string_object_no_keepalive(HashtableEntry<oop, mtSymbol>* entry) {
-  // The AS_NO_KEEPALIVE peeks at the oop without keeping it alive.
-  // This is *very dangerous* in general but is okay in this specific
-  // case. The subsequent oop_load keeps the oop alive if it it matched
-  // the jchar* string.
-  return RootAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(entry->literal_addr());
+size_t StringTable::items_to_clean(size_t ncl) {
+  size_t total = Atomic::add((size_t)ncl, &(the_table()->_uncleaned_items));
+  log_trace(stringtable)(
+     "Uncleaned items:" SIZE_FORMAT " added: " SIZE_FORMAT " total:" SIZE_FORMAT,
+     the_table()->_uncleaned_items, ncl, total);
+  return total;
 }
 
-void StringTable::set_string_object(HashtableEntry<oop, mtSymbol>* entry, oop string) {
-  RootAccess<ON_PHANTOM_OOP_REF>::oop_store(entry->literal_addr(), string);
+void StringTable::item_removed() {
+  Atomic::add((size_t)-1, &(the_table()->_items));
+  Atomic::add((size_t)-1, &(the_table()->_uncleaned_items));
 }
 
-oop StringTable::lookup_shared(jchar* name, int len, unsigned int hash) {
-  assert(hash == java_lang_String::hash_code(name, len),
-         "hash must be computed using java_lang_String::hash_code");
-  return _shared_table.lookup((const char*)name, hash, len);
+double StringTable::get_load_factor() {
+  return (_items*1.0)/_current_size;
 }
 
-oop StringTable::lookup_in_main_table(int index, jchar* name,
-                                      int len, unsigned int hash) {
-  int count = 0;
-  for (HashtableEntry<oop, mtSymbol>* l = bucket(index); l != NULL; l = l->next()) {
-    count++;
-    if (l->hash() == hash) {
-      if (java_lang_String::equals(string_object_no_keepalive(l), name, len)) {
-        // We must perform a new load with string_object() that keeps the string
-        // alive as we must expose the oop as strongly reachable when exiting
-        // this context, in case the oop gets published.
-        return string_object(l);
-      }
-    }
-  }
-  // If the bucket size is too deep check if this hash code is insufficient.
-  if (count >= rehash_count && !needs_rehashing()) {
-    _needs_rehashing = check_rehash_table(count);
-  }
-  return NULL;
+double StringTable::get_dead_factor() {
+  return (_uncleaned_items*1.0)/_current_size;
 }
 
-
-oop StringTable::basic_add(int index_arg, Handle string, jchar* name,
-                           int len, unsigned int hashValue_arg, TRAPS) {
-
-  assert(java_lang_String::equals(string(), name, len),
-         "string must be properly initialized");
-  // Cannot hit a safepoint in this function because the "this" pointer can move.
-  NoSafepointVerifier nsv;
-
-  // Check if the symbol table has been rehashed, if so, need to recalculate
-  // the hash value and index before second lookup.
-  unsigned int hashValue;
-  int index;
-  if (use_alternate_hashcode()) {
-    hashValue = alt_hash_string(name, len);
-    index = hash_to_index(hashValue);
-  } else {
-    hashValue = hashValue_arg;
-    index = index_arg;
-  }
-
-  // Since look-up was done lock-free, we need to check if another
-  // thread beat us in the race to insert the symbol.
-
-  // No need to lookup the shared table from here since the caller (intern()) already did
-  oop test = lookup_in_main_table(index, name, len, hashValue); // calls lookup(u1*, int)
-  if (test != NULL) {
-    // Entry already added
-    return test;
-  }
-
-  HashtableEntry<oop, mtSymbol>* entry = new_entry(hashValue, string());
-  add_entry(index, entry);
-  return string();
+size_t StringTable::table_size(Thread* thread) {
+  return ((size_t)(1)) << _local_table->get_size_log2(thread != NULL ? thread
+                                                      : Thread::current());
 }
 
+void StringTable::trigger_concurrent_work() {
+  MutexLockerEx ml(Service_lock, Mutex::_no_safepoint_check_flag);
+  the_table()->_has_work = true;
+  Service_lock->notify_all();
+}
 
+// Probing
 oop StringTable::lookup(Symbol* symbol) {
   ResourceMark rm;
   int length;
@@ -211,71 +239,45 @@
 }
 
 oop StringTable::lookup(jchar* name, int len) {
-  // shared table always uses java_lang_String::hash_code
   unsigned int hash = java_lang_String::hash_code(name, len);
-  oop string = lookup_shared(name, len, hash);
+  oop string = StringTable::the_table()->lookup_shared(name, len, hash);
   if (string != NULL) {
     return string;
   }
-  if (use_alternate_hashcode()) {
-    hash = alt_hash_string(name, len);
+  if (StringTable::_alt_hash) {
+    hash = hash_string(name, len, true);
   }
-  int index = the_table()->hash_to_index(hash);
-  string = the_table()->lookup_in_main_table(index, name, len, hash);
-
-  return string;
+  return StringTable::the_table()->do_lookup(name, len, hash);
 }
 
-oop StringTable::intern(Handle string_or_null, jchar* name,
-                        int len, TRAPS) {
-  // shared table always uses java_lang_String::hash_code
-  unsigned int hashValue = java_lang_String::hash_code(name, len);
-  oop found_string = lookup_shared(name, len, hashValue);
-  if (found_string != NULL) {
-    return found_string;
+class StringTableGet : public StackObj {
+  Thread* _thread;
+  Handle  _return;
+ public:
+  StringTableGet(Thread* thread) : _thread(thread) {}
+  void operator()(WeakHandle<vm_string_table_data>* val) {
+    oop result = val->resolve();
+    assert(result != NULL, "Result should be reachable");
+    _return = Handle(_thread, result);
   }
-  if (use_alternate_hashcode()) {
-    hashValue = alt_hash_string(name, len);
+  oop get_res_oop() {
+    return _return();
   }
-  int index = the_table()->hash_to_index(hashValue);
-  found_string = the_table()->lookup_in_main_table(index, name, len, hashValue);
+};
 
-  // Found
-  if (found_string != NULL) {
-    return found_string;
+oop StringTable::do_lookup(jchar* name, int len, uintx hash) {
+  Thread* thread = Thread::current();
+  StringTableLookupJchar lookup(thread, hash, name, len);
+  StringTableGet stg(thread);
+  bool rehash_warning;
+  _local_table->get(thread, lookup, stg, &rehash_warning);
+  if (rehash_warning) {
+    _needs_rehashing = true;
   }
-
-  debug_only(StableMemoryChecker smc(name, len * sizeof(name[0])));
-  assert(!Universe::heap()->is_in_reserved(name),
-         "proposed name of symbol must be stable");
-
-  HandleMark hm(THREAD);  // cleanup strings created
-  Handle string;
-  // try to reuse the string if possible
-  if (!string_or_null.is_null()) {
-    string = string_or_null;
-  } else {
-    string = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
-  }
-
-  // Deduplicate the string before it is interned. Note that we should never
-  // deduplicate a string after it has been interned. Doing so will counteract
-  // compiler optimizations done on e.g. interned string literals.
-  Universe::heap()->deduplicate_string(string());
-
-  // Grab the StringTable_lock before getting the_table() because it could
-  // change at safepoint.
-  oop added_or_found;
-  {
-    MutexLocker ml(StringTable_lock, THREAD);
-    // Otherwise, add to symbol to table
-    added_or_found = the_table()->basic_add(index, string, name, len,
-                                  hashValue, CHECK_NULL);
-  }
-
-  return added_or_found;
+  return stg.get_res_oop();
 }
 
+// Interning
 oop StringTable::intern(Symbol* symbol, TRAPS) {
   if (symbol == NULL) return NULL;
   ResourceMark rm(THREAD);
@@ -286,19 +288,17 @@
   return result;
 }
 
-
-oop StringTable::intern(oop string, TRAPS)
-{
+oop StringTable::intern(oop string, TRAPS) {
   if (string == NULL) return NULL;
   ResourceMark rm(THREAD);
   int length;
   Handle h_string (THREAD, string);
-  jchar* chars = java_lang_String::as_unicode_string(string, length, CHECK_NULL);
+  jchar* chars = java_lang_String::as_unicode_string(string, length,
+                                                     CHECK_NULL);
   oop result = intern(h_string, chars, length, CHECK_NULL);
   return result;
 }
 
-
 oop StringTable::intern(const char* utf8_string, TRAPS) {
   if (utf8_string == NULL) return NULL;
   ResourceMark rm(THREAD);
@@ -310,340 +310,449 @@
   return result;
 }
 
-void StringTable::unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
-  BucketUnlinkContext context;
-  buckets_unlink_or_oops_do(is_alive, f, 0, the_table()->table_size(), &context);
-  _the_table->bulk_free_entries(&context);
-  *processed = context._num_processed;
-  *removed = context._num_removed;
+oop StringTable::intern(Handle string_or_null_h, jchar* name, int len, TRAPS) {
+  // shared table always uses java_lang_String::hash_code
+  unsigned int hash = java_lang_String::hash_code(name, len);
+  oop found_string = StringTable::the_table()->lookup_shared(name, len, hash);
+  if (found_string != NULL) {
+    return found_string;
+  }
+  if (StringTable::_alt_hash) {
+    hash = hash_string(name, len, true);
+  }
+  return StringTable::the_table()->do_intern(string_or_null_h, name, len,
+                                             hash, CHECK_NULL);
 }
 
-void StringTable::possibly_parallel_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int* processed, int* removed) {
-  // Readers of the table are unlocked, so we should only be removing
-  // entries at a safepoint.
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
-  const int limit = the_table()->table_size();
+class StringTableCreateEntry : public StackObj {
+ private:
+   Thread* _thread;
+   Handle  _return;
+   Handle  _store;
+ public:
+  StringTableCreateEntry(Thread* thread, Handle store)
+    : _thread(thread), _store(store) {}
 
-  BucketUnlinkContext context;
-  for (;;) {
-    // Grab next set of buckets to scan
-    int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
-    if (start_idx >= limit) {
-      // End of table
-      break;
-    }
+  WeakHandle<vm_string_table_data> operator()() { // No dups found
+    WeakHandle<vm_string_table_data> wh =
+      WeakHandle<vm_string_table_data>::create(_store);
+    return wh;
+  }
+  void operator()(bool inserted, WeakHandle<vm_string_table_data>* val) {
+    oop result = val->resolve();
+    assert(result != NULL, "Result should be reachable");
+    _return = Handle(_thread, result);
+  }
+  oop get_return() const {
+    return _return();
+  }
+};
 
-    int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
-    buckets_unlink_or_oops_do(is_alive, f, start_idx, end_idx, &context);
+oop StringTable::do_intern(Handle string_or_null_h, jchar* name,
+                           int len, uintx hash, TRAPS) {
+  HandleMark hm(THREAD);  // cleanup strings created
+  Handle string_h;
+
+  if (!string_or_null_h.is_null()) {
+    string_h = string_or_null_h;
+  } else {
+    string_h = java_lang_String::create_from_unicode(name, len, CHECK_NULL);
   }
-  _the_table->bulk_free_entries(&context);
-  *processed = context._num_processed;
-  *removed = context._num_removed;
+
+  // Deduplicate the string before it is interned. Note that we should never
+  // deduplicate a string after it has been interned. Doing so will counteract
+  // compiler optimizations done on e.g. interned string literals.
+  Universe::heap()->deduplicate_string(string_h());
+
+  assert(java_lang_String::equals(string_h(), name, len),
+         "string must be properly initialized");
+  assert(len == java_lang_String::length(string_h()), "Must be same length");
+  StringTableLookupOop lookup(THREAD, hash, string_h);
+  StringTableCreateEntry stc(THREAD, string_h);
+
+  bool rehash_warning;
+  _local_table->get_insert_lazy(THREAD, lookup, stc, stc, &rehash_warning);
+  if (rehash_warning) {
+    _needs_rehashing = true;
+  }
+  return stc.get_return();
 }
 
-void StringTable::buckets_oops_do(OopClosure* f, int start_idx, int end_idx) {
-  const int limit = the_table()->table_size();
+// GC support
+class StringTableIsAliveCounter : public BoolObjectClosure {
+  BoolObjectClosure* _real_boc;
+ public:
+  size_t _count;
+  size_t _count_total;
+  StringTableIsAliveCounter(BoolObjectClosure* boc) : _real_boc(boc), _count(0),
+                                                      _count_total(0) {}
+  bool do_object_b(oop obj) {
+    bool ret = _real_boc->do_object_b(obj);
+    if (!ret) {
+      ++_count;
+    }
+    ++_count_total;
+    return ret;
+  }
+};
 
-  assert(0 <= start_idx && start_idx <= limit,
-         "start_idx (%d) is out of bounds", start_idx);
-  assert(0 <= end_idx && end_idx <= limit,
-         "end_idx (%d) is out of bounds", end_idx);
-  assert(start_idx <= end_idx,
-         "Index ordering: start_idx=%d, end_idx=%d",
-         start_idx, end_idx);
+void StringTable::unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f,
+                                    int* processed, int* removed) {
+  DoNothingClosure dnc;
+  assert(is_alive != NULL, "No closure");
+  StringTableIsAliveCounter stiac(is_alive);
+  OopClosure* tmp = f != NULL ? f : &dnc;
 
-  for (int i = start_idx; i < end_idx; i += 1) {
-    HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
-    while (entry != NULL) {
-      assert(!entry->is_shared(), "CDS not used for the StringTable");
+  StringTable::the_table()->_weak_handles->weak_oops_do(&stiac, tmp);
 
-      f->do_oop((oop*)entry->literal_addr());
-
-      entry = entry->next();
-    }
+  StringTable::the_table()->items_to_clean(stiac._count);
+  StringTable::the_table()->check_concurrent_work();
+  if (processed != NULL) {
+    *processed = (int) stiac._count_total;
   }
-}
-
-void StringTable::buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, BucketUnlinkContext* context) {
-  const int limit = the_table()->table_size();
-
-  assert(0 <= start_idx && start_idx <= limit,
-         "start_idx (%d) is out of bounds", start_idx);
-  assert(0 <= end_idx && end_idx <= limit,
-         "end_idx (%d) is out of bounds", end_idx);
-  assert(start_idx <= end_idx,
-         "Index ordering: start_idx=%d, end_idx=%d",
-         start_idx, end_idx);
-
-  for (int i = start_idx; i < end_idx; ++i) {
-    HashtableEntry<oop, mtSymbol>** p = the_table()->bucket_addr(i);
-    HashtableEntry<oop, mtSymbol>* entry = the_table()->bucket(i);
-    while (entry != NULL) {
-      assert(!entry->is_shared(), "CDS not used for the StringTable");
-
-      if (is_alive->do_object_b(string_object_no_keepalive(entry))) {
-        if (f != NULL) {
-          f->do_oop(entry->literal_addr());
-        }
-        p = entry->next_addr();
-      } else {
-        *p = entry->next();
-        context->free_entry(entry);
-      }
-      context->_num_processed++;
-      entry = *p;
-    }
+  if (removed != NULL) {
+    *removed = (int) stiac._count;
   }
 }
 
 void StringTable::oops_do(OopClosure* f) {
-  buckets_oops_do(f, 0, the_table()->table_size());
+  assert(f != NULL, "No closure");
+  StringTable::the_table()->_weak_handles->oops_do(f);
 }
 
-void StringTable::possibly_parallel_oops_do(OopClosure* f) {
-  const int limit = the_table()->table_size();
+void StringTable::possibly_parallel_unlink(
+   OopStorage::ParState<false, false>* _par_state_string, BoolObjectClosure* cl,
+   int* processed, int* removed)
+{
+  DoNothingClosure dnc;
+  assert(cl != NULL, "No closure");
+  StringTableIsAliveCounter stiac(cl);
 
-  for (;;) {
-    // Grab next set of buckets to scan
-    int start_idx = Atomic::add(ClaimChunkSize, &_parallel_claimed_idx) - ClaimChunkSize;
-    if (start_idx >= limit) {
-      // End of table
-      break;
+  _par_state_string->weak_oops_do(&stiac, &dnc);
+
+  StringTable::the_table()->items_to_clean(stiac._count);
+  StringTable::the_table()->check_concurrent_work();
+  *processed = (int) stiac._count_total;
+  *removed = (int) stiac._count;
+}
+
+void StringTable::possibly_parallel_oops_do(
+   OopStorage::ParState<false /* concurrent */, false /* const */>*
+   _par_state_string, OopClosure* f)
+{
+  assert(f != NULL, "No closure");
+  _par_state_string->oops_do(f);
+}
+
+// Concurrent work
+void StringTable::grow(JavaThread* jt) {
+  StringTableHash::GrowTask gt(_local_table);
+  if (!gt.prepare(jt)) {
+    return;
+  }
+  log_trace(stringtable)("Started to grow");
+  {
+    TraceTime timer("Grow", TRACETIME_LOG(Debug, stringtable, perf));
+    while (gt.doTask(jt)) {
+      gt.pause(jt);
+      {
+        ThreadBlockInVM tbivm(jt);
+      }
+      gt.cont(jt);
     }
+  }
+  gt.done(jt);
+  _current_size = table_size(jt);
+  log_debug(stringtable)("Grown to size:" SIZE_FORMAT, _current_size);
+}
 
-    int end_idx = MIN2(limit, start_idx + ClaimChunkSize);
-    buckets_oops_do(f, start_idx, end_idx);
+struct StringTableDoDelete : StackObj {
+  long _count;
+  StringTableDoDelete() : _count(0) {}
+  void operator()(WeakHandle<vm_string_table_data>* val) {
+    ++_count;
+  }
+};
+
+struct StringTableDeleteCheck : StackObj {
+  long _count;
+  long _item;
+  StringTableDeleteCheck() : _count(0), _item(0) {}
+  bool operator()(WeakHandle<vm_string_table_data>* val) {
+    ++_item;
+    oop tmp = val->peek();
+    if (tmp == NULL) {
+      ++_count;
+      return true;
+    } else {
+      return false;
+    }
+  }
+};
+
+void StringTable::clean_dead_entries(JavaThread* jt) {
+  StringTableHash::BulkDeleteTask bdt(_local_table);
+  if (!bdt.prepare(jt)) {
+    return;
+  }
+
+  StringTableDeleteCheck stdc;
+  StringTableDoDelete stdd;
+  bool interrupted = false;
+  {
+    TraceTime timer("Clean", TRACETIME_LOG(Debug, stringtable, perf));
+    while(bdt.doTask(jt, stdc, stdd)) {
+      bdt.pause(jt);
+      {
+        ThreadBlockInVM tbivm(jt);
+      }
+      if (!bdt.cont(jt)) {
+        interrupted = true;
+        break;
+      }
+    }
+  }
+  if (interrupted) {
+    _has_work = true;
+  } else {
+    bdt.done(jt);
+  }
+  log_debug(stringtable)("Cleaned %ld of %ld", stdc._count, stdc._item);
+}
+
+void StringTable::check_concurrent_work() {
+  if (_has_work) {
+    return;
+  }
+  double load_factor = StringTable::get_load_factor();
+  double dead_factor = StringTable::get_dead_factor();
+  // We should clean/resize if we have more dead than alive,
+  // more items than preferred load factor or
+  // more dead items than water mark.
+  if ((dead_factor > load_factor) ||
+      (load_factor > PREF_AVG_LIST_LEN) ||
+      (dead_factor > CLEAN_DEAD_HIGH_WATER_MARK)) {
+    log_debug(stringtable)("Concurrent work triggered, live factor:%g dead factor:%g",
+                           load_factor, dead_factor);
+    trigger_concurrent_work();
   }
 }
 
-// This verification is part of Universe::verify() and needs to be quick.
-// See StringTable::verify_and_compare() below for exhaustive verification.
-void StringTable::verify() {
-  for (int i = 0; i < the_table()->table_size(); ++i) {
-    HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
-    for ( ; p != NULL; p = p->next()) {
-      oop s = string_object_no_keepalive(p);
-      guarantee(s != NULL, "interned string is NULL");
-      unsigned int h = hash_string(s);
-      guarantee(p->hash() == h, "broken hash in string table entry");
-      guarantee(the_table()->hash_to_index(h) == i,
-                "wrong index in string table");
-    }
+void StringTable::concurrent_work(JavaThread* jt) {
+  _has_work = false;
+  double load_factor = get_load_factor();
+  log_debug(stringtable, perf)("Concurrent work, live factor: %g", load_factor);
+  // We prefer growing, since that also removes dead items
+  if (load_factor > PREF_AVG_LIST_LEN && !_local_table->is_max_size_reached()) {
+    grow(jt);
+  } else {
+    clean_dead_entries(jt);
   }
 }
 
-void StringTable::dump(outputStream* st, bool verbose) {
-  if (!verbose) {
-    the_table()->print_table_statistics(st, "StringTable", string_object_no_keepalive);
+void StringTable::do_concurrent_work(JavaThread* jt) {
+  StringTable::the_table()->concurrent_work(jt);
+}
+
+// Rehash
+bool StringTable::do_rehash() {
+  if (!_local_table->is_safepoint_safe()) {
+    return false;
+  }
+
+  // We use max size
+  StringTableHash* new_table = new StringTableHash(END_SIZE, END_SIZE, REHASH_LEN);
+  // Use alt hash from now on
+  _alt_hash = true;
+  if (!_local_table->try_move_nodes_to(Thread::current(), new_table)) {
+    _alt_hash = false;
+    delete new_table;
+    return false;
+  }
+
+  // free old table
+  delete _local_table;
+  _local_table = new_table;
+
+  return true;
+}
+
+void StringTable::try_rehash_table() {
+  static bool rehashed = false;
+  log_debug(stringtable)("Table imbalanced, rehashing called.");
+
+  // Grow instead of rehash.
+  if (get_load_factor() > PREF_AVG_LIST_LEN &&
+      !_local_table->is_max_size_reached()) {
+    log_debug(stringtable)("Choosing growing over rehashing.");
+    trigger_concurrent_work();
+    _needs_rehashing = false;
+    return;
+  }
+  // Already rehashed.
+  if (rehashed) {
+    log_warning(stringtable)("Rehashing already done, still long lists.");
+    trigger_concurrent_work();
+    _needs_rehashing = false;
+    return;
+  }
+
+  murmur_seed = AltHashing::compute_seed();
+  {
+    if (do_rehash()) {
+      rehashed = true;
+    } else {
+      log_info(stringtable)("Resizes in progress rehashing skipped.");
+    }
+  }
+  _needs_rehashing = false;
+}
+
+void StringTable::rehash_table() {
+  StringTable::the_table()->try_rehash_table();
+}
+
+// Statistics
+static int literal_size(oop obj) {
+  // NOTE: this would over-count if (pre-JDK8)
+  // java_lang_Class::has_offset_field() is true and the String.value array is
+  // shared by several Strings. However, starting from JDK8, the String.value
+  // array is not shared anymore.
+  if (obj == NULL) {
+    return 0;
+  } else if (obj->klass() == SystemDictionary::String_klass()) {
+    return (obj->size() + java_lang_String::value(obj)->size()) * HeapWordSize;
   } else {
-    Thread* THREAD = Thread::current();
-    st->print_cr("VERSION: 1.1");
-    for (int i = 0; i < the_table()->table_size(); ++i) {
-      HashtableEntry<oop, mtSymbol>* p = the_table()->bucket(i);
-      for ( ; p != NULL; p = p->next()) {
-        oop s = string_object_no_keepalive(p);
-        typeArrayOop value     = java_lang_String::value_no_keepalive(s);
-        int          length    = java_lang_String::length(s);
-        bool         is_latin1 = java_lang_String::is_latin1(s);
-
-        if (length <= 0) {
-          st->print("%d: ", length);
-        } else {
-          ResourceMark rm(THREAD);
-          int utf8_length = length;
-          char* utf8_string;
-
-          if (!is_latin1) {
-            jchar* chars = value->char_at_addr(0);
-            utf8_string = UNICODE::as_utf8(chars, utf8_length);
-          } else {
-            jbyte* bytes = value->byte_at_addr(0);
-            utf8_string = UNICODE::as_utf8(bytes, utf8_length);
-          }
-
-          st->print("%d: ", utf8_length);
-          HashtableTextDump::put_utf8(st, utf8_string, utf8_length);
-        }
-        st->cr();
-      }
-    }
+    return obj->size();
   }
 }
 
-StringTable::VerifyRetTypes StringTable::compare_entries(
-                                      int bkt1, int e_cnt1,
-                                      HashtableEntry<oop, mtSymbol>* e_ptr1,
-                                      int bkt2, int e_cnt2,
-                                      HashtableEntry<oop, mtSymbol>* e_ptr2) {
-  // These entries are sanity checked by verify_and_compare_entries()
-  // before this function is called.
-  oop str1 = string_object_no_keepalive(e_ptr1);
-  oop str2 = string_object_no_keepalive(e_ptr2);
+struct SizeFunc : StackObj {
+  size_t operator()(WeakHandle<vm_string_table_data>* val) {
+    oop s = val->peek();
+    if (s == NULL) {
+      // Dead
+      return 0;
+    }
+    return literal_size(s);
+  };
+};
 
-  if (str1 == str2) {
-    tty->print_cr("ERROR: identical oop values (0x" PTR_FORMAT ") "
-                  "in entry @ bucket[%d][%d] and entry @ bucket[%d][%d]",
-                  p2i(str1), bkt1, e_cnt1, bkt2, e_cnt2);
-    return _verify_fail_continue;
-  }
-
-  if (java_lang_String::equals(str1, str2)) {
-    tty->print_cr("ERROR: identical String values in entry @ "
-                  "bucket[%d][%d] and entry @ bucket[%d][%d]",
-                  bkt1, e_cnt1, bkt2, e_cnt2);
-    return _verify_fail_continue;
-  }
-
-  return _verify_pass;
+void StringTable::print_table_statistics(outputStream* st,
+                                         const char* table_name) {
+  SizeFunc sz;
+  _local_table->statistics_to(Thread::current(), sz, st, table_name);
 }
 
-StringTable::VerifyRetTypes StringTable::verify_entry(int bkt, int e_cnt,
-                                                      HashtableEntry<oop, mtSymbol>* e_ptr,
-                                                      StringTable::VerifyMesgModes mesg_mode) {
+// Verification
+class VerifyStrings : StackObj {
+ public:
+  bool operator()(WeakHandle<vm_string_table_data>* val) {
+    oop s = val->peek();
+    if (s != NULL) {
+      assert(java_lang_String::length(s) >= 0, "Length on string must work.");
+    }
+    return true;
+  };
+};
 
-  VerifyRetTypes ret = _verify_pass;  // be optimistic
-
-  oop str = string_object_no_keepalive(e_ptr);
-  if (str == NULL) {
-    if (mesg_mode == _verify_with_mesgs) {
-      tty->print_cr("ERROR: NULL oop value in entry @ bucket[%d][%d]", bkt,
-                    e_cnt);
-    }
-    // NULL oop means no more verifications are possible
-    return _verify_fail_done;
+// This verification is part of Universe::verify() and needs to be quick.
+void StringTable::verify() {
+  Thread* thr = Thread::current();
+  VerifyStrings vs;
+  if (!the_table()->_local_table->try_scan(thr, vs)) {
+    log_info(stringtable)("verify unavailable at this moment");
   }
-
-  if (str->klass() != SystemDictionary::String_klass()) {
-    if (mesg_mode == _verify_with_mesgs) {
-      tty->print_cr("ERROR: oop is not a String in entry @ bucket[%d][%d]",
-                    bkt, e_cnt);
-    }
-    // not a String means no more verifications are possible
-    return _verify_fail_done;
-  }
-
-  unsigned int h = hash_string(str);
-  if (e_ptr->hash() != h) {
-    if (mesg_mode == _verify_with_mesgs) {
-      tty->print_cr("ERROR: broken hash value in entry @ bucket[%d][%d], "
-                    "bkt_hash=%d, str_hash=%d", bkt, e_cnt, e_ptr->hash(), h);
-    }
-    ret = _verify_fail_continue;
-  }
-
-  if (the_table()->hash_to_index(h) != bkt) {
-    if (mesg_mode == _verify_with_mesgs) {
-      tty->print_cr("ERROR: wrong index value for entry @ bucket[%d][%d], "
-                    "str_hash=%d, hash_to_index=%d", bkt, e_cnt, h,
-                    the_table()->hash_to_index(h));
-    }
-    ret = _verify_fail_continue;
-  }
-
-  return ret;
 }
 
-// See StringTable::verify() above for the quick verification that is
-// part of Universe::verify(). This verification is exhaustive and
-// reports on every issue that is found. StringTable::verify() only
-// reports on the first issue that is found.
-//
-// StringTable::verify_entry() checks:
-// - oop value != NULL (same as verify())
-// - oop value is a String
-// - hash(String) == hash in entry (same as verify())
-// - index for hash == index of entry (same as verify())
-//
-// StringTable::compare_entries() checks:
-// - oops are unique across all entries
-// - String values are unique across all entries
-//
-int StringTable::verify_and_compare_entries() {
-  assert(StringTable_lock->is_locked(), "sanity check");
-
-  int  fail_cnt = 0;
-
-  // first, verify all the entries individually:
-  for (int bkt = 0; bkt < the_table()->table_size(); bkt++) {
-    HashtableEntry<oop, mtSymbol>* e_ptr = the_table()->bucket(bkt);
-    for (int e_cnt = 0; e_ptr != NULL; e_ptr = e_ptr->next(), e_cnt++) {
-      VerifyRetTypes ret = verify_entry(bkt, e_cnt, e_ptr, _verify_with_mesgs);
-      if (ret != _verify_pass) {
-        fail_cnt++;
+// Verification and comp
+class VerifyCompStrings : StackObj {
+  GrowableArray<oop>* _oops;
+ public:
+  size_t _errors;
+  VerifyCompStrings(GrowableArray<oop>* oops) : _oops(oops), _errors(0) {}
+  bool operator()(WeakHandle<vm_string_table_data>* val) {
+    oop s = val->resolve();
+    if (s == NULL) {
+      return true;
+    }
+    int len = _oops->length();
+    for (int i = 0; i < len; i++) {
+      bool eq = java_lang_String::equals(s, _oops->at(i));
+      assert(!eq, "Duplicate strings");
+      if (eq) {
+        _errors++;
       }
     }
+    _oops->push(s);
+    return true;
+  };
+};
+
+size_t StringTable::verify_and_compare_entries() {
+  Thread* thr = Thread::current();
+  GrowableArray<oop>* oops =
+    new (ResourceObj::C_HEAP, mtInternal)
+      GrowableArray<oop>((int)the_table()->_current_size, true);
+
+  VerifyCompStrings vcs(oops);
+  if (!the_table()->_local_table->try_scan(thr, vcs)) {
+    log_info(stringtable)("verify unavailable at this moment");
   }
+  delete oops;
+  return vcs._errors;
+}
 
-  // Optimization: if the above check did not find any failures, then
-  // the comparison loop below does not need to call verify_entry()
-  // before calling compare_entries(). If there were failures, then we
-  // have to call verify_entry() to see if the entry can be passed to
-  // compare_entries() safely. When we call verify_entry() in the loop
-  // below, we do so quietly to void duplicate messages and we don't
-  // increment fail_cnt because the failures have already been counted.
-  bool need_entry_verify = (fail_cnt != 0);
+// Dumping
+class PrintString : StackObj {
+  Thread* _thr;
+  outputStream* _st;
+ public:
+  PrintString(Thread* thr, outputStream* st) : _thr(thr), _st(st) {}
+  bool operator()(WeakHandle<vm_string_table_data>* val) {
+    oop s = val->peek();
+    if (s == NULL) {
+      return true;
+    }
+    typeArrayOop value     = java_lang_String::value_no_keepalive(s);
+    int          length    = java_lang_String::length(s);
+    bool         is_latin1 = java_lang_String::is_latin1(s);
 
-  // second, verify all entries relative to each other:
-  for (int bkt1 = 0; bkt1 < the_table()->table_size(); bkt1++) {
-    HashtableEntry<oop, mtSymbol>* e_ptr1 = the_table()->bucket(bkt1);
-    for (int e_cnt1 = 0; e_ptr1 != NULL; e_ptr1 = e_ptr1->next(), e_cnt1++) {
-      if (need_entry_verify) {
-        VerifyRetTypes ret = verify_entry(bkt1, e_cnt1, e_ptr1,
-                                          _verify_quietly);
-        if (ret == _verify_fail_done) {
-          // cannot use the current entry to compare against other entries
-          continue;
-        }
+    if (length <= 0) {
+      _st->print("%d: ", length);
+    } else {
+      ResourceMark rm(_thr);
+      int utf8_length = length;
+      char* utf8_string;
+
+      if (!is_latin1) {
+        jchar* chars = value->char_at_addr(0);
+        utf8_string = UNICODE::as_utf8(chars, utf8_length);
+      } else {
+        jbyte* bytes = value->byte_at_addr(0);
+        utf8_string = UNICODE::as_utf8(bytes, utf8_length);
       }
 
-      for (int bkt2 = bkt1; bkt2 < the_table()->table_size(); bkt2++) {
-        HashtableEntry<oop, mtSymbol>* e_ptr2 = the_table()->bucket(bkt2);
-        int e_cnt2;
-        for (e_cnt2 = 0; e_ptr2 != NULL; e_ptr2 = e_ptr2->next(), e_cnt2++) {
-          if (bkt1 == bkt2 && e_cnt2 <= e_cnt1) {
-            // skip the entries up to and including the one that
-            // we're comparing against
-            continue;
-          }
+      _st->print("%d: ", utf8_length);
+      HashtableTextDump::put_utf8(_st, utf8_string, utf8_length);
+    }
+    _st->cr();
+    return true;
+  };
+};
 
-          if (need_entry_verify) {
-            VerifyRetTypes ret = verify_entry(bkt2, e_cnt2, e_ptr2,
-                                              _verify_quietly);
-            if (ret == _verify_fail_done) {
-              // cannot compare against this entry
-              continue;
-            }
-          }
-
-          // compare two entries, report and count any failures:
-          if (compare_entries(bkt1, e_cnt1, e_ptr1, bkt2, e_cnt2, e_ptr2)
-              != _verify_pass) {
-            fail_cnt++;
-          }
-        }
-      }
+void StringTable::dump(outputStream* st, bool verbose) {
+  if (!verbose) {
+    the_table()->print_table_statistics(st, "StringTable");
+  } else {
+    Thread* thr = Thread::current();
+    ResourceMark rm(thr);
+    st->print_cr("VERSION: 1.1");
+    PrintString ps(thr, st);
+    if (!the_table()->_local_table->try_scan(thr, ps)) {
+      st->print_cr("dump unavailable at this moment");
     }
   }
-  return fail_cnt;
-}
-
-// Create a new table and using alternate hash code, populate the new table
-// with the existing strings.   Set flag to use the alternate hash code afterwards.
-void StringTable::rehash_table() {
-  assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
-  // This should never happen with -Xshare:dump but it might in testing mode.
-  if (DumpSharedSpaces) return;
-  StringTable* new_table = new StringTable();
-
-  // Rehash the table
-  the_table()->move_to(new_table);
-
-  // Delete the table and buckets (entries are reused in new table).
-  delete _the_table;
-  // Don't check if we need rehashing until the table gets unbalanced again.
-  // Then rehash with a new global seed.
-  _needs_rehashing = false;
-  _the_table = new_table;
 }
 
 // Utility for dumping strings
@@ -671,14 +780,21 @@
   }
 }
 
+// Sharing
 #if INCLUDE_CDS_JAVA_HEAP
-// Sharing
+oop StringTable::lookup_shared(jchar* name, int len, unsigned int hash) {
+  assert(hash == java_lang_String::hash_code(name, len),
+         "hash must be computed using java_lang_String::hash_code");
+  return _shared_table.lookup((const char*)name, hash, len);
+}
+
 oop StringTable::create_archived_string(oop s, Thread* THREAD) {
   assert(DumpSharedSpaces, "this function is only used with -Xshare:dump");
 
   oop new_s = NULL;
   typeArrayOop v = java_lang_String::value_no_keepalive(s);
-  typeArrayOop new_v = (typeArrayOop)MetaspaceShared::archive_heap_object(v, THREAD);
+  typeArrayOop new_v =
+    (typeArrayOop)MetaspaceShared::archive_heap_object(v, THREAD);
   if (new_v == NULL) {
     return NULL;
   }
@@ -692,51 +808,51 @@
   return new_s;
 }
 
-bool StringTable::copy_shared_string(GrowableArray<MemRegion> *string_space,
-                                     CompactStringTableWriter* writer) {
+struct CopyToArchive : StackObj {
+  CompactStringTableWriter* _writer;
+  CopyToArchive(CompactStringTableWriter* writer) : _writer(writer) {}
+  bool operator()(WeakHandle<vm_string_table_data>* val) {
+    oop s = val->peek();
+    if (s == NULL) {
+      return true;
+    }
+    unsigned int hash = java_lang_String::hash_code(s);
+    if (hash == 0) {
+      return true;
+    }
+
+    java_lang_String::set_hash(s, hash);
+    oop new_s = StringTable::create_archived_string(s, Thread::current());
+    if (new_s == NULL) {
+      return true;
+    }
+
+    val->replace(new_s);
+    // add to the compact table
+    _writer->add(hash, new_s);
+    return true;
+  }
+};
+
+void StringTable::copy_shared_string_table(CompactStringTableWriter* writer) {
   assert(MetaspaceShared::is_heap_object_archiving_allowed(), "must be");
 
-  Thread* THREAD = Thread::current();
-  for (int i = 0; i < the_table()->table_size(); ++i) {
-    HashtableEntry<oop, mtSymbol>* bucket = the_table()->bucket(i);
-    for ( ; bucket != NULL; bucket = bucket->next()) {
-      oop s = string_object_no_keepalive(bucket);
-      unsigned int hash = java_lang_String::hash_code(s);
-      if (hash == 0) {
-        continue;
-      }
-
-      java_lang_String::set_hash(s, hash);
-      oop new_s = create_archived_string(s, THREAD);
-      if (new_s == NULL) {
-        continue;
-      }
-
-      // set the archived string in bucket
-      set_string_object(bucket, new_s);
-
-      // add to the compact table
-      writer->add(hash, new_s);
-    }
-  }
-
-  return true;
+  CopyToArchive copy(writer);
+  StringTable::the_table()->_local_table->do_scan(Thread::current(), copy);
 }
 
-void StringTable::write_to_archive(GrowableArray<MemRegion> *string_space) {
+void StringTable::write_to_archive() {
   assert(MetaspaceShared::is_heap_object_archiving_allowed(), "must be");
 
   _shared_table.reset();
-  int num_buckets = the_table()->number_of_entries() /
-                         SharedSymbolTableBucketSize;
+  int num_buckets = the_table()->_items / SharedSymbolTableBucketSize;
   // calculation of num_buckets can result in zero buckets, we need at least one
   CompactStringTableWriter writer(num_buckets > 1 ? num_buckets : 1,
                                   &MetaspaceShared::stats()->string);
 
   // Copy the interned strings into the "string space" within the java heap
-  if (copy_shared_string(string_space, &writer)) {
-    writer.dump(&_shared_table);
-  }
+  copy_shared_string_table(&writer);
+  writer.dump(&_shared_table);
 }
 
 void StringTable::serialize(SerializeClosure* soc) {
@@ -744,7 +860,8 @@
   _shared_table.serialize(soc);
 
   if (soc->writing()) {
-    _shared_table.reset(); // Sanity. Make sure we don't use the shared table at dump time
+    // Sanity. Make sure we don't use the shared table at dump time
+    _shared_table.reset();
   } else if (!_shared_string_mapped) {
     _shared_table.reset();
   }
--- a/src/hotspot/share/classfile/stringTable.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/classfile/stringTable.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -25,109 +25,111 @@
 #ifndef SHARE_VM_CLASSFILE_STRINGTABLE_HPP
 #define SHARE_VM_CLASSFILE_STRINGTABLE_HPP
 
-#include "utilities/hashtable.hpp"
+#include "gc/shared/oopStorage.hpp"
+#include "gc/shared/oopStorageParState.hpp"
+#include "memory/allocation.hpp"
+#include "memory/padded.hpp"
+#include "oops/oop.hpp"
+#include "oops/weakHandle.hpp"
+#include "utilities/concurrentHashTable.hpp"
 
 template <class T, class N> class CompactHashtable;
 class CompactStringTableWriter;
-class FileMapInfo;
 class SerializeClosure;
 
-class StringTable : public RehashableHashtable<oop, mtSymbol> {
+class StringTable;
+class StringTableConfig;
+typedef ConcurrentHashTable<WeakHandle<vm_string_table_data>,
+                            StringTableConfig, mtSymbol> StringTableHash;
+
+class StringTableCreateEntry;
+
+class StringTable : public CHeapObj<mtSymbol>{
   friend class VMStructs;
   friend class Symbol;
+  friend class StringTableConfig;
+  friend class StringTableCreateEntry;
 
 private:
+  void grow(JavaThread* jt);
+  void clean_dead_entries(JavaThread* jt);
+
   // The string table
   static StringTable* _the_table;
-
   // Shared string table
   static CompactHashtable<oop, char> _shared_table;
   static bool _shared_string_mapped;
+  static bool _alt_hash;
+private:
 
-  // Set if one bucket is out of balance due to hash algorithm deficiency
-  static bool _needs_rehashing;
+   // Set if one bucket is out of balance due to hash algorithm deficiency
+  StringTableHash* _local_table;
+  size_t _current_size;
+  volatile bool _has_work;
+  volatile bool _needs_rehashing;
 
-  // Claimed high water mark for parallel chunked scanning
-  static volatile int _parallel_claimed_idx;
+  OopStorage* _weak_handles;
 
-  static oop intern(Handle string_or_null, jchar* chars, int length, TRAPS);
-  oop basic_add(int index, Handle string_or_null, jchar* name, int len,
-                unsigned int hashValue, TRAPS);
+  volatile size_t _items;
+  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile size_t));
+  volatile size_t _uncleaned_items;
+  DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile size_t));
 
-  oop lookup_in_main_table(int index, jchar* chars, int length, unsigned int hashValue);
-  static oop lookup_shared(jchar* name, int len, unsigned int hash);
+  double get_load_factor();
+  double get_dead_factor();
 
-  // Apply the give oop closure to the entries to the buckets
-  // in the range [start_idx, end_idx).
-  static void buckets_oops_do(OopClosure* f, int start_idx, int end_idx);
+  void check_concurrent_work();
+  void trigger_concurrent_work();
 
-  typedef StringTable::BucketUnlinkContext BucketUnlinkContext;
-  // Unlink or apply the give oop closure to the entries to the buckets
-  // in the range [start_idx, end_idx). Unlinked bucket entries are collected in the given
-  // context to be freed later.
-  // This allows multiple threads to work on the table at once.
-  static void buckets_unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f, int start_idx, int end_idx, BucketUnlinkContext* context);
+  static uintx item_added();
+  static void item_removed();
+  static size_t items_to_clean(size_t ncl);
 
-  // Hashing algorithm, used as the hash value used by the
-  //     StringTable for bucket selection and comparison (stored in the
-  //     HashtableEntry structures).  This is used in the String.intern() method.
-  static unsigned int hash_string(const jchar* s, int len);
-  static unsigned int hash_string(oop string);
-  static unsigned int alt_hash_string(const jchar* s, int len);
+  StringTable();
 
-  // Accessors for the string roots in the hashtable entries.
-  // Use string_object_no_keepalive() only when the value is not returned
-  // outside of a scope where a thread transition is possible.
-  static oop string_object(HashtableEntry<oop, mtSymbol>* entry);
-  static oop string_object_no_keepalive(HashtableEntry<oop, mtSymbol>* entry);
-  static void set_string_object(HashtableEntry<oop, mtSymbol>* entry, oop string);
+  static oop intern(Handle string_or_null_h, jchar* name, int len, TRAPS);
+  oop do_intern(Handle string_or_null, jchar* name, int len, uintx hash, TRAPS);
+  oop do_lookup(jchar* name, int len, uintx hash);
 
-  StringTable() : RehashableHashtable<oop, mtSymbol>((int)StringTableSize,
-                              sizeof (HashtableEntry<oop, mtSymbol>)) {}
+  void concurrent_work(JavaThread* jt);
+  void print_table_statistics(outputStream* st, const char* table_name);
 
-  StringTable(HashtableBucket<mtSymbol>* t, int number_of_entries)
-    : RehashableHashtable<oop, mtSymbol>((int)StringTableSize, sizeof (HashtableEntry<oop, mtSymbol>), t,
-                     number_of_entries) {}
-public:
+  void try_rehash_table();
+  bool do_rehash();
+
+ public:
   // The string table
   static StringTable* the_table() { return _the_table; }
+  size_t table_size(Thread* thread = NULL);
 
-  // Size of one bucket in the string table.  Used when checking for rollover.
-  static uint bucket_size() { return sizeof(HashtableBucket<mtSymbol>); }
+  static OopStorage* weak_storage() { return the_table()->_weak_handles; }
 
   static void create_table() {
     assert(_the_table == NULL, "One string table allowed.");
     _the_table = new StringTable();
   }
 
+  static void do_concurrent_work(JavaThread* jt);
+  static bool has_work() { return the_table()->_has_work; }
+
   // GC support
   //   Delete pointers to otherwise-unreachable objects.
-  static void unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f) {
-    int processed = 0;
-    int removed = 0;
-    unlink_or_oops_do(cl, f, &processed, &removed);
+  static void unlink(BoolObjectClosure* cl) {
+    unlink_or_oops_do(cl);
   }
-  static void unlink(BoolObjectClosure* cl) {
-    int processed = 0;
-    int removed = 0;
-    unlink_or_oops_do(cl, NULL, &processed, &removed);
-  }
-  static void unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f, int* processed, int* removed);
-  static void unlink(BoolObjectClosure* cl, int* processed, int* removed) {
-    unlink_or_oops_do(cl, NULL, processed, removed);
-  }
+  static void unlink_or_oops_do(BoolObjectClosure* is_alive, OopClosure* f = NULL,
+                                int* processed = NULL, int* removed = NULL);
+
   // Serially invoke "f->do_oop" on the locations of all oops in the table.
   static void oops_do(OopClosure* f);
 
   // Possibly parallel versions of the above
-  static void possibly_parallel_unlink_or_oops_do(BoolObjectClosure* cl, OopClosure* f, int* processed, int* removed);
-  static void possibly_parallel_unlink(BoolObjectClosure* cl, int* processed, int* removed) {
-    possibly_parallel_unlink_or_oops_do(cl, NULL, processed, removed);
-  }
-  static void possibly_parallel_oops_do(OopClosure* f);
-
-  // Internal test.
-  static void test_alt_hash() PRODUCT_RETURN;
+  static void possibly_parallel_unlink(
+     OopStorage::ParState<false /* concurrent */, false /* const*/>* par_state_string,
+     BoolObjectClosure* cl, int* processed, int* removed);
+  static void possibly_parallel_oops_do(
+     OopStorage::ParState<false /* concurrent */, false /* const*/>* par_state_string,
+     OopClosure* f);
 
   // Probing
   static oop lookup(Symbol* symbol);
@@ -138,46 +140,28 @@
   static oop intern(oop string, TRAPS);
   static oop intern(const char *utf8_string, TRAPS);
 
-  // Debugging
-  static void verify();
-  static void dump(outputStream* st, bool verbose=false);
-
-  enum VerifyMesgModes {
-    _verify_quietly    = 0,
-    _verify_with_mesgs = 1
-  };
-
-  enum VerifyRetTypes {
-    _verify_pass          = 0,
-    _verify_fail_continue = 1,
-    _verify_fail_done     = 2
-  };
-
-  static VerifyRetTypes compare_entries(int bkt1, int e_cnt1,
-                                        HashtableEntry<oop, mtSymbol>* e_ptr1,
-                                        int bkt2, int e_cnt2,
-                                        HashtableEntry<oop, mtSymbol>* e_ptr2);
-  static VerifyRetTypes verify_entry(int bkt, int e_cnt,
-                                     HashtableEntry<oop, mtSymbol>* e_ptr,
-                                     VerifyMesgModes mesg_mode);
-  static int verify_and_compare_entries();
+  // Rehash the string table if it gets out of balance
+  static void rehash_table();
+  static bool needs_rehashing()
+    { return StringTable::the_table()->_needs_rehashing; }
 
   // Sharing
+ private:
+  oop lookup_shared(jchar* name, int len, unsigned int hash) NOT_CDS_JAVA_HEAP_RETURN_(NULL);
+  static void copy_shared_string_table(CompactStringTableWriter* ch_table) NOT_CDS_JAVA_HEAP_RETURN;
+ public:
+  static oop create_archived_string(oop s, Thread* THREAD);
   static void set_shared_string_mapped() { _shared_string_mapped = true; }
   static bool shared_string_mapped()       { return _shared_string_mapped; }
   static void shared_oops_do(OopClosure* f) NOT_CDS_JAVA_HEAP_RETURN;
-  static bool copy_shared_string(GrowableArray<MemRegion> *string_space,
-                                 CompactStringTableWriter* ch_table) NOT_CDS_JAVA_HEAP_RETURN_(false);
-  static oop  create_archived_string(oop s, Thread* THREAD) NOT_CDS_JAVA_HEAP_RETURN_(NULL);
-  static void write_to_archive(GrowableArray<MemRegion> *string_space) NOT_CDS_JAVA_HEAP_RETURN;
+  static void write_to_archive() NOT_CDS_JAVA_HEAP_RETURN;
   static void serialize(SerializeClosure* soc) NOT_CDS_JAVA_HEAP_RETURN;
 
-  // Rehash the symbol table if it gets out of balance
-  static void rehash_table();
-  static bool needs_rehashing() { return _needs_rehashing; }
+  // Jcmd
+  static void dump(outputStream* st, bool verbose=false);
+  // Debugging
+  static size_t verify_and_compare_entries();
+  static void verify();
+};
 
-  // Parallel chunked scanning
-  static void clear_parallel_claimed_index() { _parallel_claimed_idx = 0; }
-  static int parallel_claimed_index() { return _parallel_claimed_idx; }
-};
 #endif // SHARE_VM_CLASSFILE_STRINGTABLE_HPP
--- a/src/hotspot/share/gc/cms/cmsHeap.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/cms/cmsHeap.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -220,13 +220,14 @@
                                 ScanningOption so,
                                 bool only_strong_roots,
                                 OopsInGenClosure* root_closure,
-                                CLDClosure* cld_closure) {
+                                CLDClosure* cld_closure,
+                                OopStorage::ParState<false, false>* par_state_string) {
   MarkingCodeBlobClosure mark_code_closure(root_closure, !CodeBlobToOopClosure::FixRelocations);
   CLDClosure* weak_cld_closure = only_strong_roots ? NULL : cld_closure;
 
   process_roots(scope, so, root_closure, cld_closure, weak_cld_closure, &mark_code_closure);
   if (!only_strong_roots) {
-    process_string_table_roots(scope, root_closure);
+    process_string_table_roots(scope, root_closure, par_state_string);
   }
 
   if (young_gen_as_roots &&
--- a/src/hotspot/share/gc/cms/cmsHeap.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/cms/cmsHeap.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -30,6 +30,7 @@
 #include "gc/shared/collectedHeap.hpp"
 #include "gc/shared/gcCause.hpp"
 #include "gc/shared/genCollectedHeap.hpp"
+#include "gc/shared/oopStorageParState.hpp"
 #include "utilities/growableArray.hpp"
 
 class CLDClosure;
@@ -90,7 +91,8 @@
                          ScanningOption so,
                          bool only_strong_roots,
                          OopsInGenClosure* root_closure,
-                         CLDClosure* cld_closure);
+                         CLDClosure* cld_closure,
+                         OopStorage::ParState<false, false>* par_state_string = NULL);
 
   GCMemoryManager* old_manager() const { return _old_manager; }
 
--- a/src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -54,6 +54,7 @@
 #include "gc/shared/genCollectedHeap.hpp"
 #include "gc/shared/genOopClosures.inline.hpp"
 #include "gc/shared/isGCActiveMark.hpp"
+#include "gc/shared/oopStorageParState.hpp"
 #include "gc/shared/referencePolicy.hpp"
 #include "gc/shared/space.inline.hpp"
 #include "gc/shared/strongRootsScope.hpp"
@@ -2769,10 +2770,12 @@
  protected:
   CMSCollector*     _collector;
   uint              _n_workers;
+  OopStorage::ParState<false, false> _par_state_string;
   CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
       AbstractGangTask(name),
       _collector(collector),
-      _n_workers(n_workers) {}
+      _n_workers(n_workers),
+      _par_state_string(StringTable::weak_storage()) {}
   // Work method in support of parallel rescan ... of young gen spaces
   void do_young_space_rescan(OopsInGenClosure* cl,
                              ContiguousSpace* space,
@@ -4274,7 +4277,9 @@
                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
                           _collector->should_unload_classes(),
                           &par_mri_cl,
-                          &cld_closure);
+                          &cld_closure,
+                          &_par_state_string);
+
   assert(_collector->should_unload_classes()
          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
@@ -4403,7 +4408,8 @@
                           GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
                           _collector->should_unload_classes(),
                           &par_mrias_cl,
-                          NULL);     // The dirty klasses will be handled below
+                          NULL,     // The dirty klasses will be handled below
+                          &_par_state_string);
 
   assert(_collector->should_unload_classes()
          || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
--- a/src/hotspot/share/gc/cms/parNewGeneration.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/cms/parNewGeneration.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -23,6 +23,7 @@
  */
 
 #include "precompiled.hpp"
+#include "classfile/stringTable.hpp"
 #include "gc/cms/cmsHeap.inline.hpp"
 #include "gc/cms/compactibleFreeListSpace.hpp"
 #include "gc/cms/concurrentMarkSweepGeneration.hpp"
@@ -589,7 +590,8 @@
     _young_gen(young_gen), _old_gen(old_gen),
     _young_old_boundary(young_old_boundary),
     _state_set(state_set),
-    _strong_roots_scope(strong_roots_scope)
+    _strong_roots_scope(strong_roots_scope),
+    _par_state_string(StringTable::weak_storage())
 {}
 
 void ParNewGenTask::work(uint worker_id) {
@@ -611,7 +613,8 @@
   heap->young_process_roots(_strong_roots_scope,
                            &par_scan_state.to_space_root_closure(),
                            &par_scan_state.older_gen_closure(),
-                           &cld_scan_closure);
+                           &cld_scan_closure,
+                           &_par_state_string);
 
   par_scan_state.end_strong_roots();
 
--- a/src/hotspot/share/gc/cms/parNewGeneration.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/cms/parNewGeneration.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -29,6 +29,7 @@
 #include "gc/serial/defNewGeneration.hpp"
 #include "gc/shared/copyFailedInfo.hpp"
 #include "gc/shared/gcTrace.hpp"
+#include "gc/shared/oopStorageParState.hpp"
 #include "gc/shared/plab.hpp"
 #include "gc/shared/preservedMarks.hpp"
 #include "gc/shared/taskqueue.hpp"
@@ -236,6 +237,7 @@
   HeapWord*                    _young_old_boundary;
   class ParScanThreadStateSet* _state_set;
   StrongRootsScope*            _strong_roots_scope;
+  OopStorage::ParState<false, false> _par_state_string;
 
 public:
   ParNewGenTask(ParNewGeneration*      young_gen,
--- a/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/g1/g1CollectedHeap.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -69,6 +69,7 @@
 #include "gc/shared/gcTraceTime.inline.hpp"
 #include "gc/shared/generationSpec.hpp"
 #include "gc/shared/isGCActiveMark.hpp"
+#include "gc/shared/oopStorageParState.hpp"
 #include "gc/shared/preservedMarks.inline.hpp"
 #include "gc/shared/suspendibleThreadSet.hpp"
 #include "gc/shared/referenceProcessor.inline.hpp"
@@ -3218,6 +3219,7 @@
 private:
   BoolObjectClosure* _is_alive;
   G1StringDedupUnlinkOrOopsDoClosure _dedup_closure;
+  OopStorage::ParState<false /* concurrent */, false /* const */> _par_state_string;
 
   int _initial_string_table_size;
   int _initial_symbol_table_size;
@@ -3237,24 +3239,19 @@
     AbstractGangTask("String/Symbol Unlinking"),
     _is_alive(is_alive),
     _dedup_closure(is_alive, NULL, false),
+    _par_state_string(StringTable::weak_storage()),
     _process_strings(process_strings), _strings_processed(0), _strings_removed(0),
     _process_symbols(process_symbols), _symbols_processed(0), _symbols_removed(0),
     _process_string_dedup(process_string_dedup) {
 
-    _initial_string_table_size = StringTable::the_table()->table_size();
+    _initial_string_table_size = (int) StringTable::the_table()->table_size();
     _initial_symbol_table_size = SymbolTable::the_table()->table_size();
-    if (process_strings) {
-      StringTable::clear_parallel_claimed_index();
-    }
     if (process_symbols) {
       SymbolTable::clear_parallel_claimed_index();
     }
   }
 
   ~G1StringAndSymbolCleaningTask() {
-    guarantee(!_process_strings || StringTable::parallel_claimed_index() >= _initial_string_table_size,
-              "claim value %d after unlink less than initial string table size %d",
-              StringTable::parallel_claimed_index(), _initial_string_table_size);
     guarantee(!_process_symbols || SymbolTable::parallel_claimed_index() >= _initial_symbol_table_size,
               "claim value %d after unlink less than initial symbol table size %d",
               SymbolTable::parallel_claimed_index(), _initial_symbol_table_size);
@@ -3273,7 +3270,7 @@
     int symbols_processed = 0;
     int symbols_removed = 0;
     if (_process_strings) {
-      StringTable::possibly_parallel_unlink(_is_alive, &strings_processed, &strings_removed);
+      StringTable::possibly_parallel_unlink(&_par_state_string, _is_alive, &strings_processed, &strings_removed);
       Atomic::add(strings_processed, &_strings_processed);
       Atomic::add(strings_removed, &_strings_removed);
     }
--- a/src/hotspot/share/gc/g1/g1RootProcessor.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/g1/g1RootProcessor.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -38,6 +38,7 @@
 #include "gc/g1/g1RootClosures.hpp"
 #include "gc/g1/g1RootProcessor.hpp"
 #include "gc/g1/heapRegion.inline.hpp"
+#include "gc/shared/oopStorageParState.hpp"
 #include "gc/shared/referenceProcessor.hpp"
 #include "gc/shared/weakProcessor.hpp"
 #include "memory/allocation.inline.hpp"
@@ -72,6 +73,7 @@
     _process_strong_tasks(G1RP_PS_NumElements),
     _srs(n_workers),
     _lock(Mutex::leaf, "G1 Root Scanning barrier lock", false, Monitor::_safepoint_check_never),
+    _par_state_string(StringTable::weak_storage()),
     _n_workers_discovered_strong_classes(0) {}
 
 void G1RootProcessor::evacuate_roots(G1ParScanThreadState* pss, uint worker_i) {
@@ -301,7 +303,7 @@
   G1GCParPhaseTimesTracker x(phase_times, G1GCPhaseTimes::StringTableRoots, worker_i);
   // All threads execute the following. A specific chunk of buckets
   // from the StringTable are the individual tasks.
-  StringTable::possibly_parallel_oops_do(closures->weak_oops());
+  StringTable::possibly_parallel_oops_do(&_par_state_string, closures->weak_oops());
 }
 
 void G1RootProcessor::process_code_cache_roots(CodeBlobClosure* code_closure,
--- a/src/hotspot/share/gc/g1/g1RootProcessor.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/g1/g1RootProcessor.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -25,6 +25,7 @@
 #ifndef SHARE_VM_GC_G1_G1ROOTPROCESSOR_HPP
 #define SHARE_VM_GC_G1_G1ROOTPROCESSOR_HPP
 
+#include "gc/shared/oopStorageParState.hpp"
 #include "gc/shared/strongRootsScope.hpp"
 #include "memory/allocation.hpp"
 #include "runtime/mutex.hpp"
@@ -49,6 +50,7 @@
   G1CollectedHeap* _g1h;
   SubTasksDone _process_strong_tasks;
   StrongRootsScope _srs;
+  OopStorage::ParState<false, false> _par_state_string;
 
   // Used to implement the Thread work barrier.
   Monitor _lock;
--- a/src/hotspot/share/gc/shared/genCollectedHeap.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/shared/genCollectedHeap.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -44,6 +44,7 @@
 #include "gc/shared/genCollectedHeap.hpp"
 #include "gc/shared/genOopClosures.inline.hpp"
 #include "gc/shared/generationSpec.hpp"
+#include "gc/shared/oopStorageParState.inline.hpp"
 #include "gc/shared/space.hpp"
 #include "gc/shared/strongRootsScope.hpp"
 #include "gc/shared/vmGCOperations.hpp"
@@ -851,12 +852,17 @@
 }
 
 void GenCollectedHeap::process_string_table_roots(StrongRootsScope* scope,
-                                                  OopClosure* root_closure) {
+                                                  OopClosure* root_closure,
+                                                  OopStorage::ParState<false, false>* par_state_string) {
   assert(root_closure != NULL, "Must be set");
   // All threads execute the following. A specific chunk of buckets
   // from the StringTable are the individual tasks.
+
+  // Either we should be single threaded or have a ParState
+  assert((scope->n_threads() <= 1) || par_state_string != NULL, "Parallel but no ParState");
+
   if (scope->n_threads() > 1) {
-    StringTable::possibly_parallel_oops_do(root_closure);
+    StringTable::possibly_parallel_oops_do(par_state_string, root_closure);
   } else {
     StringTable::oops_do(root_closure);
   }
@@ -865,12 +871,13 @@
 void GenCollectedHeap::young_process_roots(StrongRootsScope* scope,
                                            OopsInGenClosure* root_closure,
                                            OopsInGenClosure* old_gen_closure,
-                                           CLDClosure* cld_closure) {
+                                           CLDClosure* cld_closure,
+                                           OopStorage::ParState<false, false>* par_state_string) {
   MarkingCodeBlobClosure mark_code_closure(root_closure, CodeBlobToOopClosure::FixRelocations);
 
   process_roots(scope, SO_ScavengeCodeCache, root_closure,
                 cld_closure, cld_closure, &mark_code_closure);
-  process_string_table_roots(scope, root_closure);
+  process_string_table_roots(scope, root_closure, par_state_string);
 
   if (!_process_strong_tasks->is_task_claimed(GCH_PS_younger_gens)) {
     root_closure->reset_generation();
@@ -890,7 +897,8 @@
                                           ScanningOption so,
                                           bool only_strong_roots,
                                           OopsInGenClosure* root_closure,
-                                          CLDClosure* cld_closure) {
+                                          CLDClosure* cld_closure,
+                                          OopStorage::ParState<false, false>* par_state_string) {
   MarkingCodeBlobClosure mark_code_closure(root_closure, is_adjust_phase);
   CLDClosure* weak_cld_closure = only_strong_roots ? NULL : cld_closure;
 
@@ -899,7 +907,7 @@
     // We never treat the string table as roots during marking
     // for the full gc, so we only need to process it during
     // the adjust phase.
-    process_string_table_roots(scope, root_closure);
+    process_string_table_roots(scope, root_closure, par_state_string);
   }
 
   _process_strong_tasks->all_tasks_completed(scope->n_threads());
--- a/src/hotspot/share/gc/shared/genCollectedHeap.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/shared/genCollectedHeap.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -28,6 +28,7 @@
 #include "gc/shared/collectedHeap.hpp"
 #include "gc/shared/collectorPolicy.hpp"
 #include "gc/shared/generation.hpp"
+#include "gc/shared/oopStorageParState.hpp"
 #include "gc/shared/softRefGenPolicy.hpp"
 
 class AdaptiveSizePolicy;
@@ -401,7 +402,8 @@
                      CodeBlobToOopClosure* code_roots);
 
   void process_string_table_roots(StrongRootsScope* scope,
-                                  OopClosure* root_closure);
+                                  OopClosure* root_closure,
+                                  OopStorage::ParState<false, false>* par_state_string);
 
   // Accessor for memory state verification support
   NOT_PRODUCT(
@@ -415,14 +417,16 @@
   void young_process_roots(StrongRootsScope* scope,
                            OopsInGenClosure* root_closure,
                            OopsInGenClosure* old_gen_closure,
-                           CLDClosure* cld_closure);
+                           CLDClosure* cld_closure,
+                           OopStorage::ParState<false, false>* par_state_string = NULL);
 
   void full_process_roots(StrongRootsScope* scope,
                           bool is_adjust_phase,
                           ScanningOption so,
                           bool only_strong_roots,
                           OopsInGenClosure* root_closure,
-                          CLDClosure* cld_closure);
+                          CLDClosure* cld_closure,
+                          OopStorage::ParState<false, false>* par_state_string = NULL);
 
   // Apply "root_closure" to all the weak roots of the system.
   // These include JNI weak roots, string table,
--- a/src/hotspot/share/gc/shared/strongRootsScope.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/gc/shared/strongRootsScope.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -38,8 +38,6 @@
 
 StrongRootsScope::StrongRootsScope(uint n_threads) : _n_threads(n_threads) {
   Threads::change_thread_claim_parity();
-  // Zero the claimed high water mark in the StringTable
-  StringTable::clear_parallel_claimed_index();
 }
 
 StrongRootsScope::~StrongRootsScope() {
--- a/src/hotspot/share/memory/metaspaceShared.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/memory/metaspaceShared.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -1841,7 +1841,7 @@
   G1CollectedHeap::heap()->begin_archive_alloc_range();
 
   // Archive interned string objects
-  StringTable::write_to_archive(closed_archive);
+  StringTable::write_to_archive();
 
   G1CollectedHeap::heap()->end_archive_alloc_range(closed_archive,
                                                    os::vm_allocation_granularity());
--- a/src/hotspot/share/oops/weakHandle.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/oops/weakHandle.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -24,6 +24,7 @@
 
 #include "precompiled.hpp"
 #include "classfile/systemDictionary.hpp"
+#include "classfile/stringTable.hpp"
 #include "gc/shared/oopStorage.hpp"
 #include "oops/access.inline.hpp"
 #include "oops/oop.hpp"
@@ -35,6 +36,10 @@
   return SystemDictionary::vm_weak_oop_storage();
 }
 
+template <> OopStorage* WeakHandle<vm_string_table_data>::get_storage() {
+  return StringTable::weak_storage();
+}
+
 template <WeakHandleType T>
 WeakHandle<T> WeakHandle<T>::create(Handle obj) {
   assert(obj() != NULL, "no need to create weak null oop");
@@ -68,4 +73,5 @@
 
 // Provide instantiation.
 template class WeakHandle<vm_class_loader_data>;
+template class WeakHandle<vm_string_table_data>;
 
--- a/src/hotspot/share/oops/weakHandle.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/oops/weakHandle.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -39,12 +39,11 @@
 // This is the vm version of jweak but has different GC lifetimes and policies,
 // depending on the type.
 
-enum WeakHandleType { vm_class_loader_data, vm_string };
+enum WeakHandleType { vm_class_loader_data, vm_string, vm_string_table_data };
 
 template <WeakHandleType T>
 class WeakHandle {
  public:
-
  private:
   oop* _obj;
 
@@ -59,6 +58,8 @@
   void release() const;
   bool is_null() const { return _obj == NULL; }
 
+  void replace(oop with_obj);
+
   void print() const;
   void print_on(outputStream* st) const;
 };
--- a/src/hotspot/share/oops/weakHandle.inline.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/oops/weakHandle.inline.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -40,4 +40,10 @@
   return RootAccess<ON_PHANTOM_OOP_REF | AS_NO_KEEPALIVE>::oop_load(_obj);
 }
 
+template <WeakHandleType T>
+void WeakHandle<T>::replace(oop with_obj) {
+  RootAccess<ON_PHANTOM_OOP_REF>::oop_store(_obj, with_obj);
+}
+
 #endif // SHARE_VM_OOPS_WEAKHANDLE_INLINE_HPP
+
--- a/src/hotspot/share/runtime/globals.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/runtime/globals.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -2542,8 +2542,9 @@
           "Relax the access control checks in the verifier")                \
                                                                             \
   product(uintx, StringTableSize, defaultStringTableSize,                   \
-          "Number of buckets in the interned String table")                 \
-          range(minimumStringTableSize, 111*defaultStringTableSize)         \
+          "Number of buckets in the interned String table "                 \
+          "(will be rounded to nearest higher power of 2)")                 \
+          range(minimumStringTableSize, 16777216ul)                         \
                                                                             \
   experimental(uintx, SymbolTableSize, defaultSymbolTableSize,              \
           "Number of buckets in the JVM internal Symbol table")             \
--- a/src/hotspot/share/runtime/java.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/runtime/java.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -524,14 +524,9 @@
   }
 
   if (VerifyStringTableAtExit) {
-    int fail_cnt = 0;
-    {
-      MutexLocker ml(StringTable_lock);
-      fail_cnt = StringTable::verify_and_compare_entries();
-    }
-
+    size_t fail_cnt = StringTable::verify_and_compare_entries();
     if (fail_cnt != 0) {
-      tty->print_cr("ERROR: fail_cnt=%d", fail_cnt);
+      tty->print_cr("ERROR: fail_cnt=" SIZE_FORMAT, fail_cnt);
       guarantee(fail_cnt == 0, "unexpected StringTable verification failures");
     }
   }
--- a/src/hotspot/share/runtime/mutexLocker.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/runtime/mutexLocker.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -48,6 +48,8 @@
 Mutex*   JNIGlobalActive_lock         = NULL;
 Mutex*   JNIWeakAlloc_lock            = NULL;
 Mutex*   JNIWeakActive_lock           = NULL;
+Mutex*   StringTableWeakAlloc_lock    = NULL;
+Mutex*   StringTableWeakActive_lock   = NULL;
 Mutex*   JNIHandleBlockFreeList_lock  = NULL;
 Mutex*   VMWeakAlloc_lock             = NULL;
 Mutex*   VMWeakActive_lock            = NULL;
@@ -186,6 +188,9 @@
   def(VMWeakAlloc_lock             , PaddedMutex  , vmweak,      true,  Monitor::_safepoint_check_never);
   def(VMWeakActive_lock            , PaddedMutex  , vmweak-1,    true,  Monitor::_safepoint_check_never);
 
+  def(StringTableWeakAlloc_lock    , PaddedMutex  , vmweak,      true,  Monitor::_safepoint_check_never);
+  def(StringTableWeakActive_lock   , PaddedMutex  , vmweak-1,    true,  Monitor::_safepoint_check_never);
+
   if (UseConcMarkSweepGC || UseG1GC) {
     def(FullGCCount_lock           , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_never);      // in support of ExplicitGCInvokesConcurrent
   }
--- a/src/hotspot/share/runtime/mutexLocker.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/runtime/mutexLocker.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -42,6 +42,8 @@
 extern Mutex*   JNIGlobalActive_lock;            // JNI global storage active list lock
 extern Mutex*   JNIWeakAlloc_lock;               // JNI weak storage allocate list lock
 extern Mutex*   JNIWeakActive_lock;              // JNI weak storage active list lock
+extern Mutex*   StringTableWeakAlloc_lock;       // StringTable weak storage allocate list lock
+extern Mutex*   StringTableWeakActive_lock;      // STringTable weak storage active list lock
 extern Mutex*   JNIHandleBlockFreeList_lock;     // a lock on the JNI handle block free list
 extern Mutex*   VMWeakAlloc_lock;                // VM Weak Handles storage allocate list lock
 extern Mutex*   VMWeakActive_lock;               // VM Weak Handles storage active list lock
--- a/src/hotspot/share/runtime/serviceThread.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/runtime/serviceThread.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -23,6 +23,7 @@
  */
 
 #include "precompiled.hpp"
+#include "classfile/stringTable.hpp"
 #include "runtime/interfaceSupport.inline.hpp"
 #include "runtime/javaCalls.hpp"
 #include "runtime/serviceThread.hpp"
@@ -82,6 +83,7 @@
     bool has_gc_notification_event = false;
     bool has_dcmd_notification_event = false;
     bool acs_notify = false;
+    bool stringtable_work = false;
     JvmtiDeferredEvent jvmti_event;
     {
       // Need state transition ThreadBlockInVM so that this thread
@@ -98,7 +100,8 @@
       while (!(sensors_changed = LowMemoryDetector::has_pending_requests()) &&
              !(has_jvmti_events = JvmtiDeferredEventQueue::has_events()) &&
               !(has_gc_notification_event = GCNotifier::has_event()) &&
-              !(has_dcmd_notification_event = DCmdFactory::has_pending_jmx_notification())) {
+              !(has_dcmd_notification_event = DCmdFactory::has_pending_jmx_notification()) &&
+              !(stringtable_work = StringTable::has_work())) {
         // wait until one of the sensors has pending requests, or there is a
         // pending JVMTI event or JMX GC notification to post
         Service_lock->wait(Mutex::_no_safepoint_check_flag);
@@ -109,6 +112,10 @@
       }
     }
 
+    if (stringtable_work) {
+      StringTable::do_concurrent_work(jt);
+    }
+
     if (has_jvmti_events) {
       jvmti_event.post();
     }
--- a/src/hotspot/share/runtime/vmStructs.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/runtime/vmStructs.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -164,7 +164,6 @@
 typedef Hashtable<intptr_t, mtInternal>       IntptrHashtable;
 typedef Hashtable<Symbol*, mtSymbol>          SymbolHashtable;
 typedef HashtableEntry<Symbol*, mtClass>      SymbolHashtableEntry;
-typedef Hashtable<oop, mtSymbol>              StringHashtable;
 typedef Hashtable<InstanceKlass*, mtClass>       KlassHashtable;
 typedef HashtableEntry<InstanceKlass*, mtClass>  KlassHashtableEntry;
 typedef CompactHashtable<Symbol*, char>       SymbolCompactHashTable;
@@ -476,12 +475,6 @@
      static_field(SymbolTable,                 _shared_table,                                 SymbolCompactHashTable)                \
      static_field(RehashableSymbolHashtable,   _seed,                                         juint)                                 \
                                                                                                                                      \
-  /***************/                                                                                                                  \
-  /* StringTable */                                                                                                                  \
-  /***************/                                                                                                                  \
-                                                                                                                                     \
-     static_field(StringTable,                 _the_table,                                    StringTable*)                          \
-                                                                                                                                     \
   /********************/                                                                                                             \
   /* CompactHashTable */                                                                                                             \
   /********************/                                                                                                             \
@@ -1365,7 +1358,6 @@
   declare_toplevel_type(BasicHashtable<mtSymbol>)                         \
     declare_type(RehashableSymbolHashtable, BasicHashtable<mtSymbol>)     \
   declare_type(SymbolTable, SymbolHashtable)                              \
-  declare_type(StringTable, StringHashtable)                              \
     declare_type(Dictionary, KlassHashtable)                              \
   declare_toplevel_type(BasicHashtableEntry<mtInternal>)                  \
   declare_type(IntptrHashtableEntry, BasicHashtableEntry<mtInternal>)     \
--- a/src/hotspot/share/utilities/concurrentHashTable.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/utilities/concurrentHashTable.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -484,6 +484,9 @@
   void statistics_to(Thread* thread, VALUE_SIZE_FUNC& vs_f, outputStream* st,
                      const char* table_name);
 
+  // Moves all nodes from this table to to_cht
+  bool try_move_nodes_to(Thread* thread, ConcurrentHashTable<VALUE, CONFIG, F>* to_cht);
+
   // This is a Curiously Recurring Template Pattern (CRPT) interface for the
   // specialization.
   struct BaseConfig {
--- a/src/hotspot/share/utilities/concurrentHashTable.inline.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/utilities/concurrentHashTable.inline.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -293,7 +293,7 @@
 inline void ConcurrentHashTable<VALUE, CONFIG, F>::
   write_synchonize_on_visible_epoch(Thread* thread)
 {
-  assert(_resize_lock->owned_by_self(), "Re-size lock not held");
+  assert(_resize_lock_owner == thread, "Re-size lock not held");
   OrderAccess::fence(); // Prevent below load from floating up.
   // If no reader saw this version we can skip write_synchronize.
   if (OrderAccess::load_acquire(&_invisible_epoch) == thread) {
@@ -488,7 +488,7 @@
 {
   // Here we have resize lock so table is SMR safe, and there is no new
   // table. Can do this in parallel if we want.
-  assert(_resize_lock->owned_by_self(), "Re-size lock not held");
+  assert(_resize_lock_owner == thread, "Re-size lock not held");
   Node* ndel[BULK_DELETE_LIMIT];
   InternalTable* table = get_table();
   assert(start_idx < stop_idx, "Must be");
@@ -500,9 +500,9 @@
   // own read-side.
   GlobalCounter::critical_section_begin(thread);
   for (size_t bucket_it = start_idx; bucket_it < stop_idx; bucket_it++) {
-    Bucket* bucket  = _table->get_bucket(bucket_it);
+    Bucket* bucket = table->get_bucket(bucket_it);
     Bucket* prefetch_bucket = (bucket_it+1) < stop_idx ?
-                              _table->get_bucket(bucket_it+1) : NULL;
+                              table->get_bucket(bucket_it+1) : NULL;
 
     if (!HaveDeletables<IsPointer<VALUE>::value, EVALUATE_FUNC>::
         have_deletable(bucket, eval_f, prefetch_bucket)) {
@@ -695,17 +695,13 @@
   if (!try_resize_lock(thread)) {
     return false;
   }
-
-  assert(_resize_lock->owned_by_self(), "Re-size lock not held");
-
+  assert(_resize_lock_owner == thread, "Re-size lock not held");
   if (_table->_log2_size == _log2_start_size ||
       _table->_log2_size <= log2_size) {
     unlock_resize_lock(thread);
     return false;
   }
-
   _new_table = new InternalTable(_table->_log2_size - 1);
-
   return true;
 }
 
@@ -713,8 +709,7 @@
 inline void ConcurrentHashTable<VALUE, CONFIG, F>::
   internal_shrink_epilog(Thread* thread)
 {
-  assert(_resize_lock->owned_by_self(), "Re-size lock not held");
-  assert(_resize_lock_owner, "Should be locked");
+  assert(_resize_lock_owner == thread, "Re-size lock not held");
 
   InternalTable* old_table = set_table_from_new();
   _size_limit_reached = false;
@@ -771,14 +766,13 @@
   internal_shrink(Thread* thread, size_t log2_size)
 {
   if (!internal_shrink_prolog(thread, log2_size)) {
-    assert(!_resize_lock->owned_by_self(), "Re-size lock held");
+    assert(_resize_lock_owner != thread, "Re-size lock held");
     return false;
   }
-  assert(_resize_lock->owned_by_self(), "Re-size lock not held");
   assert(_resize_lock_owner == thread, "Should be locked by me");
   internal_shrink_range(thread, 0, _new_table->_size);
   internal_shrink_epilog(thread);
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
+  assert(_resize_lock_owner != thread, "Re-size lock held");
   return true;
 }
 
@@ -815,8 +809,7 @@
 inline void ConcurrentHashTable<VALUE, CONFIG, F>::
   internal_grow_epilog(Thread* thread)
 {
-  assert(_resize_lock->owned_by_self(), "Re-size lock not held");
-  assert(_resize_lock_owner, "Should be locked");
+  assert(_resize_lock_owner == thread, "Should be locked");
 
   InternalTable* old_table = set_table_from_new();
   unlock_resize_lock(thread);
@@ -835,14 +828,13 @@
   internal_grow(Thread* thread, size_t log2_size)
 {
   if (!internal_grow_prolog(thread, log2_size)) {
-    assert(!_resize_lock->owned_by_self(), "Re-size lock held");
+    assert(_resize_lock_owner != thread, "Re-size lock held");
     return false;
   }
-  assert(_resize_lock->owned_by_self(), "Re-size lock not held");
   assert(_resize_lock_owner == thread, "Should be locked by me");
   internal_grow_range(thread, 0, _table->_size);
   internal_grow_epilog(thread);
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
+  assert(_resize_lock_owner != thread, "Re-size lock held");
   return true;
 }
 
@@ -955,15 +947,13 @@
 inline void ConcurrentHashTable<VALUE, CONFIG, F>::
   do_scan_locked(Thread* thread, FUNC& scan_f)
 {
-  assert(_resize_lock->owned_by_self() ||
-         (thread->is_VM_thread() && SafepointSynchronize::is_at_safepoint()),
-         "Re-size lock not held or not VMThread at safepoint");
+  assert(_resize_lock_owner == thread, "Re-size lock not held");
   // We can do a critical section over the entire loop but that would block
   // updates for a long time. Instead we choose to block resizes.
   InternalTable* table = get_table();
-  for (size_t bucket_it = 0; bucket_it < _table->_size; bucket_it++) {
+  for (size_t bucket_it = 0; bucket_it < table->_size; bucket_it++) {
     ScopedCS cs(thread, this);
-    if (!visit_nodes(_table->get_bucket(bucket_it), scan_f)) {
+    if (!visit_nodes(table->get_bucket(bucket_it), scan_f)) {
       break; /* ends critical section */
     }
   } /* ends critical section */
@@ -1094,17 +1084,11 @@
 inline bool ConcurrentHashTable<VALUE, CONFIG, F>::
   try_scan(Thread* thread, SCAN_FUNC& scan_f)
 {
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
-  bool vm_and_safepoint = thread->is_VM_thread() &&
-                          SafepointSynchronize::is_at_safepoint();
-  if (!vm_and_safepoint && !try_resize_lock(thread)) {
+  if (!try_resize_lock(thread)) {
     return false;
   }
   do_scan_locked(thread, scan_f);
-  if (!vm_and_safepoint) {
-    unlock_resize_lock(thread);
-  }
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
+  unlock_resize_lock(thread);
   return true;
 }
 
@@ -1113,11 +1097,11 @@
 inline void ConcurrentHashTable<VALUE, CONFIG, F>::
   do_scan(Thread* thread, SCAN_FUNC& scan_f)
 {
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
+  assert(_resize_lock_owner != thread, "Re-size lock held");
   lock_resize_lock(thread);
   do_scan_locked(thread, scan_f);
   unlock_resize_lock(thread);
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
+  assert(_resize_lock_owner != thread, "Re-size lock held");
 }
 
 template <typename VALUE, typename CONFIG, MEMFLAGS F>
@@ -1126,12 +1110,11 @@
   try_bulk_delete(Thread* thread, EVALUATE_FUNC& eval_f, DELETE_FUNC& del_f)
 {
   if (!try_resize_lock(thread)) {
-    assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
     return false;
   }
   do_bulk_delete_locked(thread, eval_f, del_f);
   unlock_resize_lock(thread);
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
+  assert(_resize_lock_owner != thread, "Re-size lock held");
   return true;
 }
 
@@ -1140,11 +1123,9 @@
 inline void ConcurrentHashTable<VALUE, CONFIG, F>::
   bulk_delete(Thread* thread, EVALUATE_FUNC& eval_f, DELETE_FUNC& del_f)
 {
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
   lock_resize_lock(thread);
   do_bulk_delete_locked(thread, eval_f, del_f);
   unlock_resize_lock(thread);
-  assert(!_resize_lock->owned_by_self(), "Re-size lock not held");
 }
 
 template <typename VALUE, typename CONFIG, MEMFLAGS F>
@@ -1155,17 +1136,16 @@
 {
   NumberSeq summary;
   size_t literal_bytes = 0;
-  if ((thread->is_VM_thread() && !SafepointSynchronize::is_at_safepoint()) ||
-      (!thread->is_VM_thread() && !try_resize_lock(thread))) {
+  if (!try_resize_lock(thread)) {
     st->print_cr("statistics unavailable at this moment");
     return;
   }
 
   InternalTable* table = get_table();
-  for (size_t bucket_it = 0; bucket_it < _table->_size; bucket_it++) {
+  for (size_t bucket_it = 0; bucket_it < table->_size; bucket_it++) {
     ScopedCS cs(thread, this);
     size_t count = 0;
-    Bucket* bucket = _table->get_bucket(bucket_it);
+    Bucket* bucket = table->get_bucket(bucket_it);
     if (bucket->have_redirect() || bucket->is_locked()) {
         continue;
     }
@@ -1208,9 +1188,37 @@
   st->print_cr("Std. dev. of bucket size: %9.3f", summary.sd());
   st->print_cr("Maximum bucket size     : %9" PRIuPTR,
                (size_t)summary.maximum());
-  if (!thread->is_VM_thread()) {
-    unlock_resize_lock(thread);
+  unlock_resize_lock(thread);
+}
+
+template <typename VALUE, typename CONFIG, MEMFLAGS F>
+inline bool ConcurrentHashTable<VALUE, CONFIG, F>::
+  try_move_nodes_to(Thread* thread, ConcurrentHashTable<VALUE, CONFIG, F>* to_cht)
+{
+  if (!try_resize_lock(thread)) {
+    return false;
   }
+  assert(_new_table == NULL, "Must be NULL");
+  for (size_t bucket_it = 0; bucket_it < _table->_size; bucket_it++) {
+    Bucket* bucket = _table->get_bucket(bucket_it);
+    assert(!bucket->have_redirect() && !bucket->is_locked(), "Table must be uncontended");
+    while (bucket->first() != NULL) {
+      Node* move_node = bucket->first();
+      bool ok = bucket->cas_first(move_node->next(), move_node);
+      assert(ok, "Uncontended cas must work");
+      bool dead_hash = false;
+      size_t insert_hash = CONFIG::get_hash(*move_node->value(), &dead_hash);
+      if (!dead_hash) {
+        Bucket* insert_bucket = to_cht->get_bucket(insert_hash);
+        assert(!bucket->have_redirect() && !bucket->is_locked(), "Not bit should be present");
+        move_node->set_next(insert_bucket->first());
+        ok = insert_bucket->cas_first(move_node, insert_bucket->first());
+        assert(ok, "Uncontended cas must work");
+      }
+    }
+  }
+  unlock_resize_lock(thread);
+  return true;
 }
 
 #endif // include guard
--- a/src/hotspot/share/utilities/concurrentHashTableTasks.inline.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/utilities/concurrentHashTableTasks.inline.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -25,6 +25,7 @@
 #ifndef SHARE_UTILITIES_CONCURRENT_HASH_TABLE_TASKS_INLINE_HPP
 #define SHARE_UTILITIES_CONCURRENT_HASH_TABLE_TASKS_INLINE_HPP
 
+#include "utilities/globalDefinitions.hpp"
 #include "utilities/concurrentHashTable.inline.hpp"
 
 // This inline file contains BulkDeleteTask and GrowTasks which are both bucket
@@ -63,6 +64,7 @@
   // Calculate starting values.
   void setup() {
     _size_log2 = _cht->_table->_log2_size;
+    _task_size_log2 = MIN2(_task_size_log2, _size_log2);
     size_t tmp = _size_log2 > _task_size_log2 ?
                  _size_log2 - _task_size_log2 : 0;
     _stop_task = (((size_t)1) << tmp);
--- a/src/hotspot/share/utilities/globalDefinitions.hpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/hotspot/share/utilities/globalDefinitions.hpp	Thu Jun 07 14:11:56 2018 +0200
@@ -424,8 +424,8 @@
 //----------------------------------------------------------------------------------------------------
 // Default and minimum StringTableSize values
 
-const int defaultStringTableSize = NOT_LP64(1009) LP64_ONLY(60013);
-const int minimumStringTableSize = 1009;
+const int defaultStringTableSize = NOT_LP64(1024) LP64_ONLY(65536);
+const int minimumStringTableSize = 128;
 
 const int defaultSymbolTableSize = 20011;
 const int minimumSymbolTableSize = 1009;
--- a/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/memory/StringTable.java	Thu Jun 07 06:27:09 2018 -0400
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,77 +0,0 @@
-/*
- * Copyright (c) 2005, 2011, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- *
- */
-
-package sun.jvm.hotspot.memory;
-
-import java.io.*;
-import java.util.*;
-import sun.jvm.hotspot.debugger.*;
-import sun.jvm.hotspot.oops.*;
-import sun.jvm.hotspot.types.*;
-import sun.jvm.hotspot.runtime.*;
-import sun.jvm.hotspot.utilities.*;
-
-public class StringTable extends sun.jvm.hotspot.utilities.Hashtable {
-  static {
-    VM.registerVMInitializedObserver(new Observer() {
-        public void update(Observable o, Object data) {
-          initialize(VM.getVM().getTypeDataBase());
-        }
-      });
-  }
-
-  private static synchronized void initialize(TypeDataBase db) {
-    Type type = db.lookupType("StringTable");
-    theTableField  = type.getAddressField("_the_table");
-  }
-
-  // Fields
-  private static AddressField theTableField;
-
-  // Accessors
-  public static StringTable getTheTable() {
-    Address tmp = theTableField.getValue();
-    return (StringTable) VMObjectFactory.newObject(StringTable.class, tmp);
-  }
-
-  public StringTable(Address addr) {
-    super(addr);
-  }
-
-  public interface StringVisitor {
-    public void visit(Instance string);
-  }
-
-  public void stringsDo(StringVisitor visitor) {
-    ObjectHeap oh = VM.getVM().getObjectHeap();
-    int numBuckets = tableSize();
-    for (int i = 0; i < numBuckets; i++) {
-      for (HashtableEntry e = (HashtableEntry) bucket(i); e != null;
-           e = (HashtableEntry) e.next()) {
-        Instance s = (Instance)oh.newOop(e.literalValue().addOffsetToAsOopHandle(0));
-        visitor.visit(s);
-      }
-    }
-  }
-}
--- a/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/VM.java	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/runtime/VM.java	Thu Jun 07 14:11:56 2018 +0200
@@ -79,7 +79,6 @@
   private Universe     universe;
   private ObjectHeap   heap;
   private SymbolTable  symbols;
-  private StringTable  strings;
   private SystemDictionary dict;
   private ClassLoaderDataGraph cldGraph;
   private Threads      threads;
@@ -655,13 +654,6 @@
     return symbols;
   }
 
-  public StringTable getStringTable() {
-    if (strings == null) {
-      strings = StringTable.getTheTable();
-    }
-    return strings;
-  }
-
   public SystemDictionary getSystemDictionary() {
     if (dict == null) {
       dict = new SystemDictionary();
--- a/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/tools/HeapSummary.java	Thu Jun 07 06:27:09 2018 -0400
+++ b/src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/tools/HeapSummary.java	Thu Jun 07 14:11:56 2018 +0200
@@ -129,7 +129,6 @@
       }
 
       System.out.println();
-      printInternStringStatistics();
    }
 
    // Helper methods
@@ -258,41 +257,4 @@
          return -1;
       }
    }
-
-   private void printInternStringStatistics() {
-      class StringStat implements StringTable.StringVisitor {
-         private int count;
-         private long size;
-         private OopField stringValueField;
-
-         StringStat() {
-            VM vm = VM.getVM();
-            SystemDictionary sysDict = vm.getSystemDictionary();
-            InstanceKlass strKlass = sysDict.getStringKlass();
-            // String has a field named 'value' of type 'byte[]'.
-            stringValueField = (OopField) strKlass.findField("value", "[B");
-         }
-
-         private long stringSize(Instance instance) {
-            // We include String content in size calculation.
-            return instance.getObjectSize() +
-                   stringValueField.getValue(instance).getObjectSize();
-         }
-
-         public void visit(Instance str) {
-            count++;
-            size += stringSize(str);
-         }
-
-         public void print() {
-            System.out.println(count +
-                  " interned Strings occupying " + size + " bytes.");
-         }
-      }
-
-      StringStat stat = new StringStat();
-      StringTable strTable = VM.getVM().getStringTable();
-      strTable.stringsDo(stat);
-      stat.print();
-   }
 }
--- a/test/hotspot/gtest/utilities/test_concurrentHashtable.cpp	Thu Jun 07 06:27:09 2018 -0400
+++ b/test/hotspot/gtest/utilities/test_concurrentHashtable.cpp	Thu Jun 07 14:11:56 2018 +0200
@@ -265,6 +265,40 @@
   delete cht;
 }
 
+struct ChtCountScan {
+  size_t _count;
+  ChtCountScan() : _count(0) {}
+  bool operator()(uintptr_t* val) {
+    _count++;
+    return true; /* continue scan */
+  }
+};
+
+static void cht_move_to(Thread* thr) {
+  uintptr_t val1 = 0x2;
+  uintptr_t val2 = 0xe0000002;
+  uintptr_t val3 = 0x3;
+  SimpleTestLookup stl1(val1), stl2(val2), stl3(val3);
+  SimpleTestTable* from_cht = new SimpleTestTable();
+  EXPECT_TRUE(from_cht->insert(thr, stl1, val1)) << "Insert unique value failed.";
+  EXPECT_TRUE(from_cht->insert(thr, stl2, val2)) << "Insert unique value failed.";
+  EXPECT_TRUE(from_cht->insert(thr, stl3, val3)) << "Insert unique value failed.";
+
+  SimpleTestTable* to_cht = new SimpleTestTable();
+  EXPECT_TRUE(from_cht->try_move_nodes_to(thr, to_cht)) << "Moving nodes to new table failed";
+
+  ChtCountScan scan_old;
+  EXPECT_TRUE(from_cht->try_scan(thr, scan_old)) << "Scanning table should work.";
+  EXPECT_EQ(scan_old._count, (size_t)0) << "All items should be moved";
+
+  ChtCountScan scan_new;
+  EXPECT_TRUE(to_cht->try_scan(thr, scan_new)) << "Scanning table should work.";
+  EXPECT_EQ(scan_new._count, (size_t)3) << "All items should be moved";
+  EXPECT_TRUE(to_cht->get_copy(thr, stl1) == val1) << "Getting an inserted value should work.";
+  EXPECT_TRUE(to_cht->get_copy(thr, stl2) == val2) << "Getting an inserted value should work.";
+  EXPECT_TRUE(to_cht->get_copy(thr, stl3) == val3) << "Getting an inserted value should work.";
+}
+
 static void cht_grow(Thread* thr) {
   uintptr_t val = 0x2;
   uintptr_t val2 = 0x22;
@@ -371,6 +405,10 @@
   nomt_test_doer(cht_scan);
 }
 
+TEST_VM(ConcurrentHashTable, basic_move_to) {
+  nomt_test_doer(cht_move_to);
+}
+
 TEST_VM(ConcurrentHashTable, basic_grow) {
   nomt_test_doer(cht_grow);
 }